can: 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>
diff --git a/drivers/net/can/grcan.c b/drivers/net/can/grcan.c
index fed1bbd..e3d7e22 100644
--- a/drivers/net/can/grcan.c
+++ b/drivers/net/can/grcan.c
@@ -1725,7 +1725,7 @@
 	return 0;
 }
 
-static struct of_device_id grcan_match[] = {
+static const struct of_device_id grcan_match[] = {
 	{.name = "GAISLER_GRCAN"},
 	{.name = "01_03d"},
 	{.name = "GAISLER_GRHCAN"},