ALSA: hda - Mute the right widget in auto_mute_via_amp mode

The current generic parser code assumes that always a pin widget
controls the mute for an output blindly although it might be a
different widget in the middle.  Instead of the fixed assumption,
check each parsed path and just pick up the right widget that has been
already defined as a mute control.

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