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>
diff --git a/arch/powerpc/sysdev/fsl_msi.c b/arch/powerpc/sysdev/fsl_msi.c
index f4fd95b..0c01deb 100644
--- a/arch/powerpc/sysdev/fsl_msi.c
+++ b/arch/powerpc/sysdev/fsl_msi.c
@@ -74,7 +74,7 @@
 	return 0;
 }
 
-static struct irq_domain_ops fsl_msi_host_ops = {
+static const struct irq_domain_ops fsl_msi_host_ops = {
 	.map = fsl_msi_host_map,
 };