PCI: Fix NULL pointer dereference in of_pci_bus_find_domain_nr()

If the "parent" pointer passed to of_pci_bus_find_domain_nr() is NULL,
don't dereference it.
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/pci.c

@@ -5611,8 +5611,9 @@ static int of_pci_bus_find_domain_nr(struct device *parent)
 		use_dt_domains = 0;
 		domain = pci_get_new_domain_nr();
 	} else {
-		dev_err(parent, "Node %pOF has inconsistent \"linux,pci-domain\" property in DT\n",
-			parent->of_node);
+		if (parent)
+			pr_err("Node %pOF has ", parent->of_node);
+		pr_err("Inconsistent \"linux,pci-domain\" property in DT\n");
 		domain = -1;
 	}