ALSA: hda - Disable fallback to model=acer for Acer laptops

The model=acer for ALC883/889 doesn't work well for the recent Acer
Aspire laptops.  Since model=auto works better nowadays, it's safer
to use the default fallback instead of the Acer specific one.

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