ALSA: HDA: Use model=auto for LG R510

Two users report model=auto is needed to make the internal mic work properly.
BugLink: https://bugs.launchpad.net/bugs/495134



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