alc662 series only have 3 DAC, so it can only support 5stack-dig
instead of 6stack-dig.

[updated HD-Audio-Models.txt as well by tiwai]
Signed-off-by: Raymond Yau <superquad.vortex2@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>