[non-BE] Resolve "McMASA LFE synthesis has wrong subframe index"

• Related issues: #2497 (closed)
• Requested reviewers: @lintervo

Reason why this change is needed

• There is a porting error resulting in wrong subframe index.

Description of the change

• Fix the error.

Affected operating points

• Only decoder output
• McMASA bitrates 13.2-48 kbps when there is LFE content in audio and output is to loudspeakers.

Closes #2497 (closed)