ALSA: hda - Fix missing Master volume for STAC9200/925x

commit ab548d2dba63ba947287965e525cc02a15d9853d upstream.

With the commit [2faa3bf: ALSA: hda - Rewrite the mute-LED hook with
vmaster hook in patch_sigmatel.c], the former Master volume control
was converted to PCM.  This was supposed to be covered by the vmaster
control.  But due to the lack of "PCM" slave definition, this didn't
happen properly.  The patch fixes the missing entry.

Reported-by: Andrew Shadura <bugzilla@tut.by>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>