PCI: Refactor pci_bus_assign_domain_nr() for CONFIG_PCI_DOMAINS_GENERIC

Instead of assigning bus->domain_nr inside pci_bus_assign_domain_nr(),
return the domain and let the caller do the assignment.  Rename
pci_bus_assign_domain_nr() to pci_bus_find_domain_nr() to reflect this.

No functional change intended.

[bhelgaas: changelog]
Signed-off-by: Tomasz Nowicki <tn@semihalf.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
diff --git a/include/linux/pci.h b/include/linux/pci.h
index ce03d65..48839e8 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1390,12 +1390,7 @@
 {
 	return bus->domain_nr;
 }
-void pci_bus_assign_domain_nr(struct pci_bus *bus, struct device *parent);
-#else
-static inline void pci_bus_assign_domain_nr(struct pci_bus *bus,
-					struct device *parent)
-{
-}
+int pci_bus_find_domain_nr(struct pci_bus *bus, struct device *parent);
 #endif
 
 /* some architectures require additional setup to direct VGA traffic */