ALSA: oxfw: allow PCM capture for Stanton SCS.1m

Stanton SCS.1m can transfer isochronous packet with Multi Bit Linear
Audio data channels, therefore it allows software to capture PCM
substream. However, ALSA oxfw driver doesn't.

This commit changes the driver to add one PCM substream for capture
direction.

Fixes: de5126cc

 ("ALSA: oxfw: add stream format quirk for SCS.1 models")
Cc: <stable@vger.kernel.org> # v4.5+
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>