dock_remove() calls kfree() on dock_station so we should use
list_for_each_entry_safe() to avoid dereferencing freed memory.
Found by smatch (http://repo.or.cz/w/smatch.git/).  Compile tested.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Len Brown <len.brown@intel.com>
 static void __exit dock_exit(void)
 {
        struct dock_station *dock_station;
+       struct dock_station *tmp;
 
        unregister_acpi_bus_notifier(&dock_acpi_notifier);
-       list_for_each_entry(dock_station, &dock_stations, sibiling)
+       list_for_each_entry_safe(dock_station, tmp, &dock_stations, sibiling)
                dock_remove(dock_station);
 }