lvgl: dev-7.0 new styles visual studio compilation error

@kisvegabor it is unbelievable how much is being achieved by littlevgl!

Tonight I pulled the lastest code, recreated a visual studio project with the new examples and the compiler complained about this cast to return ‘(value_type)’.

Error (active) E0119 cast to type “lv_color_t” is not allowed lvgl\src\lv_core\lv_obj.h 1066

I simply removed the cast and it compiled.

#define _LV_OBJ_STYLE_SET_GET_DECLARE(prop_name, func_name, value_type, style_type)          \
static inline value_type lv_obj_get_style_##func_name (const lv_obj_t * obj, uint8_t part)  \
{                                                                                           \
    return (value_type) _lv_obj_get_style##style_type (obj, part, LV_STYLE_##prop_name);     \