PCI: fix wrong assumption in pci_common_swizzle

Current pci_common_swizzle() seems to have a assumption that
pci_bus->self is NULL on the pci root bus. But it might not be true on
some platforms. Because of this wrong assumption, pci_common_swizzle()
might cause endless loop. We must check pci_bus->parent instead.
Signed-off-by: NKenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>

drivers/pci/pci.c

@@ -1504,7 +1504,7 @@ u8 pci_common_swizzle(struct pci_dev *dev, u8 *pinp)
 {
 	u8 pin = *pinp;
 
-	while (dev->bus->self) {
+	while (dev->bus->parent) {
 		pin = pci_swizzle_interrupt_pin(dev, pin);
 		dev = dev->bus->self;
 	}