[ALSA] hda-codec - Control SPDIF as slave

Add SPDIF playback switch to the slave element list so that it
can be toggled via the master control as well.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>
diff --git a/sound/pci/hda/patch_realtek.c b/sound/pci/hda/patch_realtek.c
index 8621c9f..586d98f 100644
--- a/sound/pci/hda/patch_realtek.c
+++ b/sound/pci/hda/patch_realtek.c
@@ -1492,6 +1492,7 @@
 	"Headphone Playback Switch",
 	"Speaker Playback Switch",
 	"Mono Playback Switch",
+	"IEC958 Playback Switch",
 	NULL,
 };