ALSA: Fix workaround for AD1988A rev2 codec

Fix the workaround for AD1988A rev2 codec not to apply to AD1988B codec
chips.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>
Signed-off-by: Adrian Bunk <bunk@stusta.de>