ALSA: hda - Enable SPDIF for Acer TravelMate 6293

BIOS on Acer TravelMate 6293 doesn't set up the SPDIF output pin
correctly as default, so enable it via a fixup entry.

Reported-and-tested-by: Hagen Heiduck <heiduck.suse@fmail.postpro.net>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>