harmonization of modif_fs

Basic info

• Float reference:
  • Encoder (float):
  • Decoder (float):
• Fixed point:
  • Encoder (fixed): 244fba7c
  • Decoder (fixed): 244fba7c

Bug description

Most of modif_fs_fx and modif_fs_ivas_fx are the same, can easily be harmonized

Ways to reproduce

Box folder: ...\Box_EXTERNAL_IVAS_BASOP_VERIFICATION\issues\issue-xxxx