ALSA: hda: Add speaker pin to automute Acer Aspire 8943G

BugLink: https://bugs.launchpad.net/bugs/656625



Add clause for handling Acer Aspire 8943G's subwoofer as additional
speaker pin for automuting.

Reported-by: RussianNeuroMancer
Cc: stable@kernel.org
Signed-off-by: Daniel T Chen <crimsun@ubuntu.com>
Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>