ivas_mdct_core_tns_ns_fx(): Calculation of subframe-length overly complex

Bug description

In ivas_mdct_core_tns_ns_fx() the subframe lengths are calculated using BASOP_Util_Divide3216_Scale(), especially given that nSubframes[ch] is either 1 or 2.

L_frame_global[ch] = BASOP_Util_Divide3216_Scale( st->L_frame, nSubframes[ch], &exp );
move16();
L_frame_global[ch] = shl( L_frame_global[ch], add( exp, 1 ) );
move16();

L_frameTCX_glob[ch] = BASOP_Util_Divide3216_Scale( st->hTcxDec->L_frameTCX, nSubframes[ch], &exp );
move16();
L_frameTCX_glob[ch] = shl( L_frameTCX_glob[ch], add( exp, 1 ) );
move16();

L_spec[ch] = BASOP_Util_Divide3216_Scale( st->hTcxCfg->tcx_coded_lines, nSubframes[ch], &exp );
move16();
L_spec[ch] = shl( L_spec[ch], add( exp, 1 ) );
move16();