PCI hotplug: Fix unexpected driver unregister in pciehp_acpi.c

If pcie_ports_disabled is set, pcie_port_service_register() returns
error code and select_detection_mode() should not attempt to
unregister dummy_driver and use dummy_slots.  It should return
PCIEHP_DETECT_ACPI immediately instead.
Reviewed-by: NKenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Acked-by: NKenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>

drivers/pci/hotplug/pciehp_acpi.c

@@ -115,7 +115,8 @@ static struct pcie_port_service_driver __initdata dummy_driver = {
 static int __init select_detection_mode(void)
 {
 	struct dummy_slot *slot, *tmp;
-	pcie_port_service_register(&dummy_driver);
+	if (pcie_port_service_register(&dummy_driver))
+		return PCIEHP_DETECT_ACPI;
 	pcie_port_service_unregister(&dummy_driver);
 	list_for_each_entry_safe(slot, tmp, &dummy_slots, list) {
 		list_del(&slot->list);