ALSA: usb-audio: add support for M-Audio FT C600

Adds quirks and mixer support for the M-Audio Fast Track C600 USB
audio interface. This device is very similar to the C400 - the C600
simply has some more inputs and outputs, so the existing C400 support
is extended to support this device as well.

Signed-off-by: Matt Gruskin <matthew.gruskin@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index e90daf8..638e7f7 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -807,6 +807,7 @@
 {
 	switch (cval->mixer->chip->usb_id) {
 	case USB_ID(0x0763, 0x2030): /* M-Audio Fast Track C400 */
+	case USB_ID(0x0763, 0x2031): /* M-Audio Fast Track C600 */
 		if (strcmp(kctl->id.name, "Effect Duration") == 0) {
 			cval->min = 0x0000;
 			cval->max = 0xffff;