rt2x00: fix cancelling uninitialized work

{rx,tx}done_work's are only initialized for usb devices.
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: stable@kernel.org
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2x00dev.c

@@ -1062,8 +1062,10 @@ void rt2x00lib_remove_dev(struct rt2x00_dev *rt2x00dev)
 	 * Stop all work.
 	 */
 	cancel_work_sync(&rt2x00dev->intf_work);
-	cancel_work_sync(&rt2x00dev->rxdone_work);
-	cancel_work_sync(&rt2x00dev->txdone_work);
+	if (rt2x00_is_usb(rt2x00dev)) {
+		cancel_work_sync(&rt2x00dev->rxdone_work);
+		cancel_work_sync(&rt2x00dev->txdone_work);
+	}
 	destroy_workqueue(rt2x00dev->workqueue);
 
 	/*