ALSA: Fix missing array terminators in AD1988 codec support

Fixed the missing array terminators in AD1988 codec support code.

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