usb: gadget: gr_udc: Make of_device_id array const

Make of_device_id array const, because all OF functions handle
it as const.

Acked-by: Andreas Larsson <andreas@gaisler.com>
Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/gadget/gr_udc.c b/drivers/usb/gadget/gr_udc.c
index 99a37ed..5d93f2b 100644
--- a/drivers/usb/gadget/gr_udc.c
+++ b/drivers/usb/gadget/gr_udc.c
@@ -2212,7 +2212,7 @@
 	return retval;
 }
 
-static struct of_device_id gr_match[] = {
+static const struct of_device_id gr_match[] = {
 	{.name = "GAISLER_USBDC"},
 	{.name = "01_021"},
 	{},