dell-laptop: Fix small memory leak

da_tokens was not being freed by dell-laptop on unload. Fix that.
Signed-off-by: Matthew Garrett <mjg@redhat.com>

drivers/platform/x86/dell-laptop.c

@@ -478,6 +478,7 @@ static void __exit dell_exit(void)
 		platform_device_del(platform_device);
 		platform_driver_unregister(&platform_driver);
 	}
+	kfree(da_tokens);
 }
 
 module_init(dell_init);