ALSA: usbusx2y: constify usb_device_id.

usb_device_id are not supposed to change at runtime. All functions
working with usb_device_id provided by <linux/usb.h> work with
const usb_device_id. So mark the non-const structs as const.
Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/usx2y/usbusx2y.c

@@ -313,7 +313,7 @@ static void usX2Y_unlinkSeq(struct snd_usX2Y_AsyncSeq *S)
 }
 
 
-static struct usb_device_id snd_usX2Y_usb_id_table[] = {
+static const struct usb_device_id snd_usX2Y_usb_id_table[] = {
 	{
 		.match_flags =	USB_DEVICE_ID_MATCH_DEVICE,
 		.idVendor =	0x1604,