gpio: Constify irq_domain_ops

The irq_domain_ops are not modified by the driver and the irqdomain core
code accepts pointer to a const data.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski.k@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/drivers/gpio/gpio-bcm-kona.c b/drivers/gpio/gpio-bcm-kona.c
index b164ce8..cb89f37 100644
--- a/drivers/gpio/gpio-bcm-kona.c
+++ b/drivers/gpio/gpio-bcm-kona.c
@@ -534,7 +534,7 @@
 	irq_set_chip_data(irq, NULL);
 }
 
-static struct irq_domain_ops bcm_kona_irq_ops = {
+static const struct irq_domain_ops bcm_kona_irq_ops = {
 	.map = bcm_kona_gpio_irq_map,
 	.unmap = bcm_kona_gpio_irq_unmap,
 	.xlate = irq_domain_xlate_twocell,