ALSA: snd-usb-caiaq: 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/caiaq/device.c

@@ -81,7 +81,7 @@ enum {
 	DEPTH_32	= 3
 };
 
-static struct usb_device_id snd_usb_id_table[] = {
+static const struct usb_device_id snd_usb_id_table[] = {
 	{
 		.match_flags =	USB_DEVICE_ID_MATCH_DEVICE,
 		.idVendor =	USB_VID_NATIVEINSTRUMENTS,