carl9170: 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/ath/carl9170/usb.c

@@ -64,7 +64,7 @@ MODULE_ALIAS("arusb_lnx");
  * http://wireless.kernel.org/en/users/Drivers/ar9170/devices ),
  * whenever you add a new device.
  */
-static struct usb_device_id carl9170_usb_ids[] = {
+static const struct usb_device_id carl9170_usb_ids[] = {
 	/* Atheros 9170 */
 	{ USB_DEVICE(0x0cf3, 0x9170) },
 	/* Atheros TG121N */