ivas_osba_stereo_add_channels() differs between ivas-main and ivas-float-update

Basic info

while looking into !2521 , it has been found that the function ivas_osba_stereo_add_channels() has less code in ivas-main compared to ivas-float-update. The basop follows ivas-float-update, thus needs to be updated accordingly.

I set the priority to major as I don't know if the ISM_mode is constant for this function. if the ISM_mode is constant, then it is only clean-up and priority could be set down to minimum.

@pihlajakuja for awareness

Bug description