ALSA: bcd2000: 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/bcd2000/bcd2000.c

@@ -29,7 +29,7 @@
 #define PREFIX "snd-bcd2000: "
 #define BUFSIZE 64
 
-static struct usb_device_id id_table[] = {
+static const struct usb_device_id id_table[] = {
 	{ USB_DEVICE(0x1397, 0x00bd) },
 	{ },
 };