ACPI / PCI: Make bus registration and unregistration symmetric

Since acpi_pci_slot_enumerate() and acpiphp_enumerate_slots() can get
the ACPI device handle they need from bus->bridge, it is not
necessary to pass that handle to them as an argument.

Drop the second argument of acpi_pci_slot_enumerate() and
acpiphp_enumerate_slots(), rework them to obtain the ACPI handle
from bus->bridge and make acpi_pci_add_bus() and
acpi_pci_remove_bus() entirely symmetrical.

Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>
diff --git a/drivers/acpi/pci_slot.c b/drivers/acpi/pci_slot.c
index 033d117..d678a18 100644
--- a/drivers/acpi/pci_slot.c
+++ b/drivers/acpi/pci_slot.c
@@ -159,12 +159,16 @@
 	return AE_OK;
 }
 
-void acpi_pci_slot_enumerate(struct pci_bus *bus, acpi_handle handle)
+void acpi_pci_slot_enumerate(struct pci_bus *bus)
 {
-	mutex_lock(&slot_list_lock);
-	acpi_walk_namespace(ACPI_TYPE_DEVICE, handle, 1,
-			    register_slot, NULL, bus, NULL);
-	mutex_unlock(&slot_list_lock);
+	acpi_handle handle = ACPI_HANDLE(bus->bridge);
+
+	if (handle) {
+		mutex_lock(&slot_list_lock);
+		acpi_walk_namespace(ACPI_TYPE_DEVICE, handle, 1,
+				    register_slot, NULL, bus, NULL);
+		mutex_unlock(&slot_list_lock);
+	}
 }
 
 void acpi_pci_slot_remove(struct pci_bus *bus)