mfd: Use to_platform_device instead of container_of

Convert mfd_remove_devices_fn() to use to_platform_device()
instead of doing container_of().
Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Acked-by: Dmitry Baryshkov <dbaryshkov@gmail.com>
Signed-off-by: Samuel Ortiz <sameo@openedhand.com>

drivers/mfd/mfd-core.c

@@ -99,8 +99,7 @@ EXPORT_SYMBOL(mfd_add_devices);
 
 static int mfd_remove_devices_fn(struct device *dev, void *unused)
 {
-	platform_device_unregister(
-			container_of(dev, struct platform_device, dev));
+	platform_device_unregister(to_platform_device(dev));
 	return 0;
 }