Resolve "harmonization of the 0 bit bwe between EVS and IVAS"

• Related issues: #2350 (closed)
• Requested reviewers:

Reason why this change is needed

• harmonization of the 0 bit bwe between EVS and IVAS

Description of the change

• Simplify calling of hf_synth_fx()

Affected operating points

• All is BE.

Closes #2350 (closed)