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: NRay Jui <rjui@broadcom.com>
Reviewed-by: NScott Branden <sbranden@broadcom.com>
Reviewed-by: NRobin Murphy <robin.murphy@arm.com>
Signed-off-by: NAnup Patel <anup.patel@broadcom.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

drivers/iommu/of_iommu.c

@@ -110,6 +110,7 @@ void of_iommu_set_ops(struct device_node *np, struct iommu_ops *ops)
 	if (WARN_ON(!iommu))
 		return;
 
+	of_node_get(np);
 	INIT_LIST_HEAD(&iommu->list);
 	iommu->np = np;
 	iommu->ops = ops;