ACPI: bus: Ensure that notify handlers are not running after removal

Currently, acpi_device_remove_notify_handler() may return while the
notify handler being removed is still running which may allow the
module holding that handler to be torn down prematurely.

Address this issue by making acpi_device_remove_notify_handler() wait
for the handling of all the ACPI events in progress to complete before
returning.

Fixes: 5894b0c4 ("ACPI / scan: Move bus operations and notification routines to bus.c")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/bus.c

@@ -589,6 +589,7 @@ static void acpi_device_remove_notify_handler(struct acpi_device *device,
 		acpi_remove_notify_handler(device->handle, type,
 					   acpi_notify_device);
 	}
+	acpi_os_wait_events_complete();
 }
 
 /* Handle events targeting \_SB device (at present only graceful shutdown) */