DESC:TECHNICAL FIELD The present subject matter described herein, in general, relates to a heating assembly for an aerosol-generating device, and more particularly the invention relates to the aerosol-generating device which is an electrically operated smoking device. BACKGROUND There is an increasing demand for handheld aerosol-generating devices that are able to deliver aerosol for user inhalation. One particular area of demand is for heated smoking devices in which an aerosol-forming substrate is heated to release volatile flavour compounds, without combustion of the aerosol-forming substrate. The released volatile compounds are conveyed within an aerosol to the user. Attempts have been made to provide alternatives to these smoking articles by creating products which release compounds without creating tobacco smoke. Electronic vaporizers also known as electronic cigarettes and electronic cigars, were thus developed as an alternative solution and are becoming increasingly popular all over the world. Electrically operated smoking devices are termed as ‘healthy replacements’ to conventional cigarettes since they release compounds by heating, but not burning, tobacco and additionally give a wide variety of appealing flavour choices. Electrically operated smoking devices are battery operated units generally comprising a battery, the atomizing/vaporizing unit, and a cartridge comprising a supply of aerosol-forming substrate. A cartridge comprising both a supply of aerosol-forming substrate and a vaporizer is sometimes referred to as a “cartomizer”. The vaporizer vaporizes the aerosol-forming substrate which is in contact with a heating coil element to provide an aerosol. Control electronics control the activation of the vaporizer. When a puff is detected, the control electronics supplies electrical power to the vaporizer thereby vaporizing the substrate to an aerosol. Tobacco heating is one of the key focus of developments in an aerosol-generating system, wherein the aim is to deliver aerosol rather than following the conventional route of burning the tobacco. One of the means to supply heat to the tobacco is by electrical heating. An aerosol- generating device configured with a heater assembly that receives the aerosol-generating article can be heated either directly or indirectly by converting the electrical energy to thermal energy. Direct heating helps in effective utilization of the heat generated. However, in such an assembly, achieving the required operating temperature in a short duration is challenging. Furthermore, the distal end of the tobacco rod may be damaged due to overheating. One of the means of achieving direct heating is by inserting the heater into the tobacco substrate. However, during this process, the heater may get damaged due to the excessive force applied while inserting the tobacco substrate. Furthermore, the conventional flat shaped heater does not provide a high area of contact of the heater with the substrate. It is therefore desirable to provide a heating assembly for an aerosol-generating device which achieves a uniform operating temperature in a short duration, prevents overheating at the distal end of the tobacco rod, provides mechanical stability and prevents damage to the heater while inserting into the aerosol-forming substrate and increases the area of contact of the heater with the aerosol-forming substrate. Various types of heating assembly for generating aerosol in an aerosol-generating device are known in the art. WO 2014102092 A1 published on July 3, 2014 discloses a heating assembly for heating an aerosol-forming substrate, comprising: a heater comprising an electrically resistive heating element and a heater substrate; and a heater mount coupled to the heater; wherein the heating element comprises a first portion and a second portion configured such that, when an electrical current is passed through the heating element the first portion is heated to a higher temperature than the second portion. The heating element may also comprise a third portion configured for electrical connection to power supply. WO 2016156103 A1 published on October 6, 2016 discloses a heating assembly for heating an aerosol-forming substrate, comprising: a heater comprising an electrically resistive heating element and a heater substrate; and a heater mount coupled to the heater; wherein the first portion of the heating element is heated to a higher temperature than the second portion, and wherein the second portion of the electrically resistive heating element is longer than the first portion of the electrically resistive heating element. It may also comprise a third portion configured for electrical connection to power supply. WO 2011079933 A1 published on July 7, 2011 relates to a heater for heating an aerosol-forming substrate, the heater comprising a plurality of elongate heating elements arranged in an elongate array having a support end with a first dimension, a heating end with a second dimension and a middle portion with a third dimension, the array arranged to heat the substrate to form an aerosol, wherein the third dimension is greater than the first dimension and greater than the second dimension. However design and construction of the heating assembly used in the conventional aerosol-generating devices suffer from many drawbacks such as difficulty to achieve an uniform operating temperature in a short duration, overheating at the distal end of the tobacco rod, uneven heat distribution throughout the substrate, damage to the heater while inserting into the aerosol-forming substrate, difficulty in providing a high area of contact of the flat-shaped heater with the substrate , lack of robustness, strength and complexity in design. The present inventors have surprisingly developed a heating assembly for an aerosol-generating device that ameliorates the aforementioned shortcomings of the prior art. SUMMARY OF THE INVENTION The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later. An objective of the present invention is to provide a heating assembly for an aerosol-generating device that achieves a uniform operating temperature in a short duration. Another objective of the present invention is to provide a heating assembly for an aerosol-generating device that prevents overheating at the distal end of an aerosol-generating article. Another objective of the present invention is to provide a heating assembly for an aerosol-generating device that provides mechanical stability and prevents damage to the heater while inserting into the aerosol-forming substrate. Another objective of the present invention is to provide a heating assembly for an aerosol-generating device that increases the area of contact of the heater with the aerosol-forming substrate. Another objective of the present invention is to provide a heating assembly for an aerosol-generating device that provides a uniform heat distribution throughout the aerosol-forming substrate present within an aerosol-generating article and maintains a controlled temperature. Yet another objective of the present invention is to provide a heating assembly for an aerosol-generating device which has a simple, effective, high strength, robust design and is inexpensive to manufacture. Accordingly, to one aspect, the present invention provides a heating assembly for an aerosol-generating device configured to receive an aerosol-generating article, the heating assembly comprising: a heater having a curved base with a radius of curvature and a resistive heating element positioned across length of the heater base, wherein the resistive heating element further comprises of a first zone, a second zone and a third zone configured such that, when an electrical current is passed through the heating element, the first zone is heated to a lower temperature than the second zone and the second zone is heated to a higher temperature than the third zone. In another aspect, the present invention provides an electrically operated aerosol-generating device configured to receive an aerosol-generating article comprising: a tubular housing that receives an aerosol-generating article comprising an aerosol-forming substrate; a heating assembly within the housing further comprising: a heater having a curved base with a radius of curvature and a resistive heating element positioned across length of the heater base, wherein the resistive heating element further comprises of a first zone, a second zone and a third zone configured such that, when an electrical current is passed through the heating element, the first zone is heated to a lower temperature than the second zone and the second zone is heated to a higher temperature than the third zone; a power source within the housing; a control circuit board operably connected to a heater assembly and the power source for controlling power supplied to the heating assembly. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which: Figure 1 illustrates schematic representation of an aerosol-generating device that receives an aerosol-generating article comprising an aerosol-forming substrate, in accordance to an embodiment of the present invention. Figure 2 illustrates an enlarged view of the heating assembly in accordance to the present invention Figure 3 illustrates an internal view of the heater according to an embodiment of the present invention. Figure 4 illustrates the internal view of the heater according to another embodiment of the present invention. Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures. DETAILED DESCRIPTION OF THE PRESENT INVENTION The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness. The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide. Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments. It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. It is also to be understood that the term “module” is used in the specification to indicate an apparatus, unit, component and the like. The term “means” when used in the specification is taken to specify the mode by which desired result is achieved. The present invention relates to a heating assembly for an aerosol-generating device. In particular, the invention relates to handheld aerosol-generating device, such as an electrically operated smoking device. The term ‘aerosol-generating device' relates to a device that interacts with an aerosol-forming substrate to generate an aerosol. The aerosol-forming substrate forms a part of an aerosol-generating article, for example part of a smoking article. An aerosol-generating device may be a smoking device that interacts with an aerosol-forming substrate of an aerosol-generating article to generate an inhalable aerosol. The term 'aerosol-forming substrate' relates to a substrate capable of releasing volatile compounds that can form an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate. An aerosol-forming substrate forms a part of an aerosol-generating article or smoking article. The terms 'aerosol-generating article' and 'smoking article' refer to an article comprising an aerosol-forming substrate that is capable of releasing volatile compounds that can form an aerosol. For example, an aerosol-generating article may be a smoking article that generates an aerosol to the user. An aerosol-generating article may be disposable. The term ‘aerosol-generating system’ is a combination of an aerosol-generating device and one or more aerosol-generating articles for use with the device. The present invention relates to a heating assembly for an aerosol-generating device configured to receive an aerosol-generating article, wherein the said heating assembly comprises: i. A heater comprising a heater base and a resistive heating element positioned across the length of the said heater base; and ii. A heater mount comprising air channels, to which the said heater is mounted; wherein the said heater base is curved; wherein the said resistive heating element comprises a first zone, a second zone and a third zone configured such that, when an electrical current is passed through the said heating element, the first zone is heated to a lower temperature than the second zone and the second zone is heated to a higher temperature than the third zone. The characteristic features/ advantages of the heating assembly of the present invention to be used in an aerosol-generating device are: • The heater of the present invention covers three different temperature zones (first zone, second zone, and third zone) via the heating element designed with resistive elements in each zone. The resistive element is coated/printed/formed with a desired pattern that covers the area of the heater base; thereby helping to achieve a uniform operating temperature throughout the heater base within a short duration. • When an electrical current is passed through the heating element, the first zone is heated to a lower temperature than the second zone and the second zone is heated to a higher temperature than the third zone. This prevents overheating at the distal end of the tobacco rod. • Therefore, in the present invention, the said first zone and third zone always experience a lesser temperature than the second zone. At the same time, the first zone and third zone shall have either equivalent temperature or differential temperatures but always lesser than the second zone. This is shown in a simple representation, viz. T1, T3