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: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 0cfed9e..8310dc2 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1504,7 +1504,7 @@
 {
 	u8 pin = *pinp;
 
-	while (dev->bus->self) {
+	while (dev->bus->parent) {
 		pin = pci_swizzle_interrupt_pin(dev, pin);
 		dev = dev->bus->self;
 	}