ALSA: hda - Change pin-ctl for auto-muting in patch_via.c

Mute the outputs via pin-controls instead of amps for the auto-mute
handling.  This makes our life easier as it avoids conflict of the states
between the mixer elements and the auto-mute toggles.

With this change, we can use vmaster for the master control easily now.

Signed-off-by: Takashi Iwai <tiwai@suse.de>