net: greth: 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: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/aeroflex/greth.c

@@ -1588,7 +1588,7 @@ static int greth_of_remove(struct platform_device *of_dev)
 	return 0;
 }
 
-static struct of_device_id greth_of_match[] = {
+static const struct of_device_id greth_of_match[] = {
 	{
 	 .name = "GAISLER_ETHMAC",
 	 },