of: iommu: Increment DT node refcount in of_iommu_set_ops()

We are saving pointer to iommu DT node in of_iommu_set_ops()
hence we should increment DT node ref count.

Reviewed-by: Ray Jui <rjui@broadcom.com>
Reviewed-by: Scott Branden <sbranden@broadcom.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Anup Patel <anup.patel@broadcom.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
index 60ba238..5fea665 100644
--- a/drivers/iommu/of_iommu.c
+++ b/drivers/iommu/of_iommu.c
@@ -110,6 +110,7 @@
 	if (WARN_ON(!iommu))
 		return;
 
+	of_node_get(np);
 	INIT_LIST_HEAD(&iommu->list);
 	iommu->np = np;
 	iommu->ops = ops;