ALSA: hda - Fix (yet more) STAC925x issues

The codec-parsing of STAC925x was utterly broken due to its unique
design unlike other STAC codecs.  It has a volume control only in NID
0x0e (similar as STAC9200), but the parser assumes that the amp is
available on each DAC widget.

The patch fixes the whole wrong stories: fix the initial volume,
assign the fixed "Master" volume, and avoid to create wrong volume
controls.

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