irq_domain/powerpc: constify irq_domain_ops

Make all the irq_domain_ops structures in powerpc 'static const'

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Milton Miller <miltonm@bga.com>
Tested-by: Olof Johansson <olof@lixom.net>

arch/powerpc/sysdev/cpm1.c

@@ -123,7 +123,7 @@ static struct irqaction cpm_error_irqaction = {
 	.name = "error",
 };
 
-static struct irq_domain_ops cpm_pic_host_ops = {
+static const struct irq_domain_ops cpm_pic_host_ops = {
 	.map = cpm_pic_host_map,
 };