[ALSA] intel8x0: Add quirk for Optiplex GX270

Modules: Intel8x0 driver

This patch adds a quirk entry for the Dell Optiplex GX270, on which
the volume is set by the headphone control, not the master control.

Signed-off-by: Chris Ball <cjb@mrao.cam.ac.uk>
Signed-off-by: Takashi Iwai <tiwai@suse.de>