PCI: fix wrong assumption in pci_get_interrupt_pin

Current pci_get_interrupt_pin() seems to have an assumption that
pci_bus->self is NULL on the root pci bus. But it might not be true on
some platforms. Because of this wrong assumption, current
pci_get_interrupt_pin() 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

@@ -1484,7 +1484,7 @@ pci_get_interrupt_pin(struct pci_dev *dev, struct pci_dev **bridge)
 	if (!pin)
 		return -1;
 
-	while (dev->bus->self) {
+	while (dev->bus->parent) {
 		pin = pci_swizzle_interrupt_pin(dev, pin);
 		dev = dev->bus->self;
 	}