[ALSA] hda-codec - Add SPDIF controls as slave on AD codecs

The AD codecs have hardware SPDIF volume/switch controls but they
are not assigned to the slave list for virtual master controls.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>