According to the bug reporter, model=auto is needed to make the
internal microphone work.

BugLink: https://bugs.launchpad.net/bugs/819699
Reported-by: Andrej (agno01)
Signed-off-by: NDavid Henningsson <david.henningsson@canonical.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>