Stereo DMX formal issues

The following formal issues were identified in the stereo DMX file ivas_stereo_dmx_evs.c:

1. double-precision mathematic functions should be replaced by single-precision ones, e.g. (float) sqrt() -> sqrtf()
2. Unnecessary data type conversion statements should be removed: (float) inv_sqrt() -> inv_sqrtf()
3. Constant STEREO_DMX_EVS_SHIFT_LIMIT should be replaced by STEREO_DFT_ZP_NS_ENC and constructions like (int16_t) ( STEREO_DMX_EVS_SHIFT_LIMIT * input_Fs / 1000 ) by NS2SA()