[ALSA] Enable stereo line input for TAS codec

Despite what the data sheet says in one place, to get stereo input
from input A (line in), we have to clear the 'input B monaural' bit in
the ACR.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>