IVAS internal error in decoder for custom loudspeaker format with SBA input at >= 24.4kbps

Can be reproduced by encoding SBA input at > 24.4kbps and then decoding to a custom loudspeaker layout.

audioCfg2channels is called in lib_dec\ivas_spar_foa_dec.c:979 with output_config of AUDIO_CONFIG_LS_CUSTOM which results in IVAS_ERR_INTERNAL "Error: illegal output configuration".

The call to audioCfg2channels should be replaced with already defined variable eg. st_ivas->hDecoderConfig->nchan_out.