In the case where we have both line out and more than stereo speakers,
the speaker DACs will end up in extra_out_nid.
In fact, AFAIU, speakers are the only ones that can end up in extra_out_nid,
and if we have several of those, they should be surround outputs
rather than copy front.

BugLink: https://bugs.launchpad.net/bugs/1236965Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>