ALSA: wss_lib: snd_wss_calibrate_mute improvement

Mute sound by setting mute bit without
setting volume to 0. It makes both source code
and binary shorter.

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>