gpio: mpc8xxx: constify of_device_id

This variable is not modified in the driver and all functions it it
passed to don't change it either. So it can and should be marked const.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/drivers/gpio/gpio-mpc8xxx.c b/drivers/gpio/gpio-mpc8xxx.c
index da8e892..0e2dbbb 100644
--- a/drivers/gpio/gpio-mpc8xxx.c
+++ b/drivers/gpio/gpio-mpc8xxx.c
@@ -334,7 +334,7 @@
 	.xlate	= irq_domain_xlate_twocell,
 };
 
-static struct of_device_id mpc8xxx_gpio_ids[] = {
+static const struct of_device_id mpc8xxx_gpio_ids[] = {
 	{ .compatible = "fsl,mpc8349-gpio", },
 	{ .compatible = "fsl,mpc8572-gpio", },
 	{ .compatible = "fsl,mpc8610-gpio", },