MIPS: PCI: Fix pcibios_scan_bus() NULL check code path

If pci_scan_root_bus() fails (ie returns NULL) pcibios_scan_bus() must
return immediately since the struct pci_bus pointer it returns is not valid
and cannot be used.

Move code checking the pci_scan_root_bus() return value to reinstate proper
pcibios_scanbus() error path behaviour.

Fixes: 88555b4 ("MIPS: PCI: Support for CONFIG_PCI_DOMAINS_GENERIC")
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Burton <paul.burton@imgtec.com>

arch/mips/pci/pci-legacy.c

@@ -89,16 +89,16 @@ static void pcibios_scanbus(struct pci_controller *hose)
 	pci_add_resource(&resources, hose->busn_resource);
 	bus = pci_scan_root_bus(NULL, next_busno, hose->pci_ops, hose,
 				&resources);
-	hose->bus = bus;
-
-	need_domain_info = need_domain_info || pci_domain_nr(bus);
-	set_pci_need_domain_info(hose, need_domain_info);
-
 	if (!bus) {
 		pci_free_resource_list(&resources);
 		return;
 	}
 
+	hose->bus = bus;
+
+	need_domain_info = need_domain_info || pci_domain_nr(bus);
+	set_pci_need_domain_info(hose, need_domain_info);
+
 	next_busno = bus->busn_res.end + 1;
 	/* Don't allow 8-bit bus number overflow inside the hose -
 	   reserve some space for bridges. */