gpio: grgpio: Make of_device_id array const

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

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Andreas Larsson <andreas@gaisler.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/drivers/gpio/gpio-grgpio.c b/drivers/gpio/gpio-grgpio.c
index 84d2478..3c3f515 100644
--- a/drivers/gpio/gpio-grgpio.c
+++ b/drivers/gpio/gpio-grgpio.c
@@ -481,7 +481,7 @@
 	return ret;
 }
 
-static struct of_device_id grgpio_match[] = {
+static const struct of_device_id grgpio_match[] = {
 	{.name = "GAISLER_GPIO"},
 	{.name = "01_01a"},
 	{},