ALSA: usb - Creative USB X-Fi volume knob support

Adds an entry for Creative USB X-Fi to the rc_config array in
mixer_quirks.c to allow use of volume knob on the device.
The action of the volume knob is received by lirc when its using the
alsa_usb driver.

Signed-off-by: Mandar Joshi <emailmandar@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>