at76c50x: 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: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/atmel/at76c50x-usb.c

@@ -130,7 +130,7 @@ MODULE_FIRMWARE("atmel_at76c505amx-rfmd.bin");
 
 #define USB_DEVICE_DATA(__ops)	.driver_info = (kernel_ulong_t)(__ops)
 
-static struct usb_device_id dev_table[] = {
+static const struct usb_device_id dev_table[] = {
 	/*
 	 * at76c503-i3861
 	 */