ALSA: hda - Fix mute control with some ALC262 models

The master mute switch is wrongly implemented as checking the pointer
instead of its value, thus it can be never muted.  This patch fixes
the issue.

Reference: Novell bnc#404873
	https://bugzilla.novell.com/show_bug.cgi?id=404873

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Cc: <stable@kernel.org>