x86/events/amd/iommu: Make iommu_pmu const and __initconst

iommu_pmu is only used as source for a copy operation in the init code
path.

Mark it const and __initconst.
Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: julia.lawall@lip6.fr
Link: https://lkml.kernel.org/r/1505819443-670-1-git-send-email-bhumirks@gmail.com

arch/x86/events/amd/iommu.c

@@ -405,7 +405,7 @@ const struct attribute_group *amd_iommu_attr_groups[] = {
 	NULL,
 };
 
-static struct pmu iommu_pmu = {
+static const struct pmu iommu_pmu __initconst = {
 	.event_init	= perf_iommu_event_init,
 	.add		= perf_iommu_add,
 	.del		= perf_iommu_del,