ALSA: HDA: Realtek: Take vmaster dac from multiout dac list

With the auto-parser we can choose the dac nid for vmaster from
the DACs we already know, instead of hard-coding it. This is more
future-proof and was actually wrong on one machine.

Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>