ALSA: usb-audio: Enable S/PDIF on the ASUS Xonar U3

The only required change is to extend the existing Xonar U1
mixer quirks to the U3, which seems to be controlled the same
way.

Signed-off-by: Denis Washington <denisw@online.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/usb/mixer_quirks.c b/sound/usb/mixer_quirks.c
index bf28a1b..0422b13 100644
--- a/sound/usb/mixer_quirks.c
+++ b/sound/usb/mixer_quirks.c
@@ -430,6 +430,8 @@
 	}
 }
 
+/* ASUS Xonar U1 / U3 controls */
+
 static int snd_xonar_u1_switch_get(struct snd_kcontrol *kcontrol,
 				   struct snd_ctl_elem_value *ucontrol)
 {
@@ -1305,8 +1307,9 @@
 		err = snd_ftu_create_mixer(mixer);
 		break;
 
-	case USB_ID(0x0b05, 0x1739):
-	case USB_ID(0x0b05, 0x1743):
+	case USB_ID(0x0b05, 0x1739): /* ASUS Xonar U1 */
+	case USB_ID(0x0b05, 0x1743): /* ASUS Xonar U1 (2) */
+	case USB_ID(0x0b05, 0x17a0): /* ASUS Xonar U3 */
 		err = snd_xonar_u1_controls_create(mixer);
 		break;