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: Kenji Kaneshige <[e-mail]>
Signed-off-by: Jesse Barnes <[e-mail]>

drivers/pci/search.c

···
 	if (pdev->is_pcie)
 		return NULL;
 	while (1) {
-		if (!pdev->bus->self)
+		if (!pdev->bus->parent)
 			break;
 		pdev = pdev->bus->self;
 		/* a p2p bridge */