iommu/mediatek: Make mtk_iommu_pm_ops static

The symbol exists elsewhere already, so that is fails to
link if the symbol is non-static.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
diff --git a/drivers/iommu/mtk_iommu_v1.c b/drivers/iommu/mtk_iommu_v1.c
index 294485d..b8aeb07 100644
--- a/drivers/iommu/mtk_iommu_v1.c
+++ b/drivers/iommu/mtk_iommu_v1.c
@@ -695,7 +695,7 @@
 	return 0;
 }
 
-const struct dev_pm_ops mtk_iommu_pm_ops = {
+static const struct dev_pm_ops mtk_iommu_pm_ops = {
 	SET_SYSTEM_SLEEP_PM_OPS(mtk_iommu_suspend, mtk_iommu_resume)
 };