ALSA: hda - Fix missing mute controls for CX5051

We've added a fake mute control (setting the amp volume to zero) for
CX5051 at commit [3868137e: ALSA: hda - Add a fake mute feature], but
this feature was overlooked in the generic parser implementation.  Now
the driver lacks of mute controls on these codecs.

The fix is just to check both AC_AMPCAP_MUTE and AC_AMPCAP_MIN_MUTE
bits in each place checking the amp capabilities.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=59001
Cc: <stable@vger.kernel.org> [v3.9+]
Signed-off-by: Takashi Iwai <tiwai@suse.de>