video: fbdev: udlfb: 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 <[e-mail]>
Cc: Steve Glendinning <[e-mail]>
Cc: Bernie Thompson <[e-mail]>
Signed-off-by: Bartlomiej Zolnierkiewicz <[e-mail]>

drivers/video/fbdev/udlfb.c

···
  * which is compatible with all known USB 2.0 era graphics chips and firmware,
  * but allows DisplayLink to increment those for any future incompatible chips
  */
-static struct usb_device_id id_table[] = {
+static const struct usb_device_id id_table[] = {
 	{.idVendor = 0x17e9,
 	 .bInterfaceClass = 0xff,
 	 .bInterfaceSubClass = 0x00,