mfd: Constify regmap and irq configuration data

Constify in various drivers configuration data which is not modified:
 - regmap_irq_chip,
 - individual regmap_irq's in array,
 - regmap_config,
 - irq_domain_ops,

Signed-off-by: Krzysztof Kozlowski <k.kozlowski.k@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
diff --git a/drivers/mfd/max8998-irq.c b/drivers/mfd/max8998-irq.c
index c469477..3702056 100644
--- a/drivers/mfd/max8998-irq.c
+++ b/drivers/mfd/max8998-irq.c
@@ -214,7 +214,7 @@
 	return 0;
 }
 
-static struct irq_domain_ops max8998_irq_domain_ops = {
+static const struct irq_domain_ops max8998_irq_domain_ops = {
 	.map = max8998_irq_domain_map,
 };