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>

drivers/gpio/gpio-grgpio.c

@@ -481,7 +481,7 @@ out:
 	return ret;
 }
 
-static struct of_device_id grgpio_match[] = {
+static const struct of_device_id grgpio_match[] = {
 	{.name = "GAISLER_GPIO"},
 	{.name = "01_01a"},
 	{},