[ALSA] usb-audio - add Extigy/Audigy 2 NX remote control support

ALSA Core,USB generic driver
Add an hwdep interface that supports reading remote control data from
Sound Blaster Extigy and Audigy 2 NX devices.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
diff --git a/include/sound/asound.h b/include/sound/asound.h
index 26db585..4321e92 100644
--- a/include/sound/asound.h
+++ b/include/sound/asound.h
@@ -113,9 +113,10 @@
 	SNDRV_HWDEP_IFACE_BLUETOOTH,	/* Bluetooth audio */
 	SNDRV_HWDEP_IFACE_USX2Y_PCM,	/* Tascam US122, US224 & US428 rawusb pcm */
 	SNDRV_HWDEP_IFACE_PCXHR,	/* Digigram PCXHR */
+	SNDRV_HWDEP_IFACE_SB_RC,	/* SB Extigy/Audigy2NX remote control */
 
 	/* Don't forget to change the following: */
-	SNDRV_HWDEP_IFACE_LAST = SNDRV_HWDEP_IFACE_PCXHR
+	SNDRV_HWDEP_IFACE_LAST = SNDRV_HWDEP_IFACE_SB_RC
 };
 
 struct sndrv_hwdep_info {