hFbMixer handle at the encoder

Using the code-base SHA-1: 30b12f8d from September 9, 2022, there was observed that the handle hFbMixer->pFb is used only partially (4% encoder).

• ivas_FB_mixer_open 213 m:sizeof( ivas_filterbank_t ) - 4% 2x1854 3708

hFbMixer->pFb = (ivas_filterbank_t *) count_malloc( sizeof( ivas_filterbank_t ) )

Observed for non-SBA operation modes such as e.g. for MC at 13.2 kbps encoder, ISM 24.4 kbps encoder, or SBA 13.2 kbps encoder.

Can it be lowered?