ALSA: trident - pause s/pdif output

Stop the S/PDIF DMA engine and output when the device is told to pause.
It will keep on looping the current buffer contents if this isn't done.

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>
Tested-by: Rene Herman <rene.herman@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>