ALSA: hda - Fix empty DAC filling in patch_via.c

In via_auto_fill_adc_nids(), the parser tries to fill dac_nids[] at
the point of the current line-out (i).  When no valid path is found
for this output, this results in dac = 0, thus it creates a hole in
dac_nids[].  This confuses is_empty_dac() and trims the detected DAC
in later reference.

This patch fixes the bug by appending DAC properly to dac_nids[] in
via_auto_fill_adc_nids().

Reported-by: Massimo Del Fedele <max@veneto.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>