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: NUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-mpc8xxx.c

@@ -334,7 +334,7 @@ static const struct irq_domain_ops mpc8xxx_gpio_irq_ops = {
 	.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", },