Resolve "malloc insufficient size in ivas_mct_dec_fx"

• Related issues: #2287 (closed)
• Requested reviewers: @multrus

Reason why this change is needed

• malloc for mdcts stereo DEcoder struct uses size for mdct ystereo ENcoder struct due to typo

Description of the change

• fix the typo to correct the size for malloc

Affected operating points

• (hopefully) none

Closes #2287 (closed)