ALSA: hda - Fix PCM reference NID for STAC/IDT analog outputs

The reference NID for the analog outputs of STAC/IDT codecs is set
to a fixed number 0x02.  But this isn't always correct and in many
codecs it points to a non-existing NID.

This patch fixes the initialization of the PCM reference NID taken
from the actually probed DAC list.

Signed-off-by: Takashi Iwai <tiwai@suse.de>