pinctrl: single: 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/pinctrl/pinctrl-single.c b/drivers/pinctrl/pinctrl-single.c
index 13b45f2..968e352 100644
--- a/drivers/pinctrl/pinctrl-single.c
+++ b/drivers/pinctrl/pinctrl-single.c
@@ -1726,7 +1726,7 @@
 	return 0;
 }
 
-static struct irq_domain_ops pcs_irqdomain_ops = {
+static const struct irq_domain_ops pcs_irqdomain_ops = {
 	.map = pcs_irqdomain_map,
 	.xlate = irq_domain_xlate_onecell,
 };