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_maps.c b/sound/usb/mixer_maps.c
index 0e2ed3d..cc2dd1f 100644
--- a/sound/usb/mixer_maps.c
+++ b/sound/usb/mixer_maps.c
@@ -380,6 +380,10 @@
 		.selector_map = c400_selectors,
 	},
 	{
+		.id = USB_ID(0x0763, 0x2031),
+		.selector_map = c400_selectors,
+	},
+	{
 		.id = USB_ID(0x08bb, 0x2702),
 		.map = linex_map,
 		.ignore_ctl_error = 1,