ALSA: hda - Fix DAC checks for VT2002P/1802/1812 codecs

For VT2002P, VT1802 and VT1812 codecs, there're only two DACs. So smart51
control shouldn't be created.

Signed-off-by: Lydia Wang <lydiawang@viatech.com.cn>
Signed-off-by: Takashi Iwai <tiwai@suse.de>