usb: gadget: constify of_device_id array

of_device_id is always used as const.
(See driver.of_match_table and open firmware functions)

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/udc/pxa27x_udc.c

@@ -2387,7 +2387,7 @@ static struct pxa_udc memory = {
 };
 
 #if defined(CONFIG_OF)
-static struct of_device_id udc_pxa_dt_ids[] = {
+static const struct of_device_id udc_pxa_dt_ids[] = {
 	{ .compatible = "marvell,pxa270-udc" },
 	{}
 };