[ALSA] hda-codec - Add array terminator for dmic in STAC codec

Reported by Jan-Marek Glogowski.
The dmic array is passed to snd_hda_parse_pin_def_config() and
should be zero-terminated.

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