powerpc/eeh: Reworked eeh_pe_bus_get()

The original implementation is ugly: unnecessary if statements and
"out" tag. This reworks the function to avoid above weaknesses. No
functional changes introduced.
Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/eeh_pe.c

@@ -920,25 +920,21 @@ const char *eeh_pe_loc_get(struct eeh_pe *pe)
  */
 struct pci_bus *eeh_pe_bus_get(struct eeh_pe *pe)
 {
-	struct pci_bus *bus = NULL;
 	struct eeh_dev *edev;
 	struct pci_dev *pdev;
 
-	if (pe->type & EEH_PE_PHB) {
-		bus = pe->phb->bus;
-	} else if (pe->type & EEH_PE_BUS ||
-		   pe->type & EEH_PE_DEVICE) {
-		if (pe->state & EEH_PE_PRI_BUS) {
-			bus = pe->bus;
-			goto out;
-		}
+	if (pe->type & EEH_PE_PHB)
+		return pe->phb->bus;
+
+	/* The primary bus might be cached during probe time */
+	if (pe->state & EEH_PE_PRI_BUS)
+		return pe->bus;
 
-		edev = list_first_entry(&pe->edevs, struct eeh_dev, list);
+	/* Retrieve the parent PCI bus of first (top) PCI device */
+	edev = list_first_entry_or_null(&pe->edevs, struct eeh_dev, list);
 	pdev = eeh_dev_to_pci_dev(edev);
 	if (pdev)
-			bus = pdev->bus;
-	}
+		return pdev->bus;
 
-out:
-	return bus;
+	return NULL;
 }