PCI: fix wrong assumption in pci_find_upstream_pcie_bridge

Current pci_find_upstream_pcie_bridge() has a wrong assumption that
pci_bus->self is NULL on the root pci bus. But it might not true on
some platforms. Because of this wrong assumption, current
pci_find_upstream_pcie_bridge() 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/search.c

@@ -29,7 +29,7 @@ pci_find_upstream_pcie_bridge(struct pci_dev *pdev)
 	if (pdev->is_pcie)
 		return NULL;
 	while (1) {
-		if (!pdev->bus->self)
+		if (!pdev->bus->parent)
 			break;
 		pdev = pdev->bus->self;
 		/* a p2p bridge */