Some BIOS report invalid pins as digital output pins.  The driver checks
the connection but it doesn't do it fully correctly, and it leaves some
undefined value as the audio-out widget, which makes the driver spewing
warnings.  This patch fixes the issue.

Reference: https://bugzilla.novell.com/show_bug.cgi?id=727348

Cc: <stable@kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>