[ALSA] hda - Fix model for Acer Aspire 5720z

Set the proper model=acer for Acer Aspire 5720z with ALC268 codec.
ALSA bug#3550:
	https://bugtrack.alsa-project.org/alsa-bug/view.php?id=3550



Signed-off-by: Takashi Iwai <tiwai@suse.de>