ALSA: hda - Mute all aamix inputs as default

commit ebb93c057dda376414fbc499ad6ace9b527dff5a upstream.

Not all channels have been initialized, so far, especially when aamix
NID itself doesn't have amps but its leaves have.  This patch fixes
these holes.  Otherwise you might get unexpected loopback inputs,
e.g. from surround channels.

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