[SCSI] add missing attribute container function prototype

attribute_container_classdev_to_container is an exported function of the
attribute_container.c file.  However, there's no prototype for it.  Now
I actually want to use it, so add one.
Signed-off-by: NJames Bottomley <James.Bottomley@SteelEye.com>

include/linux/attribute_container.h

@@ -64,6 +64,7 @@ int attribute_container_add_class_device_adapter(struct attribute_container *con
 						 struct class_device *classdev);
 void attribute_container_remove_attrs(struct class_device *classdev);
 void attribute_container_class_device_del(struct class_device *classdev);
+struct attribute_container *attribute_container_classdev_to_container(struct class_device *);
 struct class_device *attribute_container_find_class_device(struct attribute_container *, struct device *);
 struct class_device_attribute **attribute_container_classdev_to_attrs(const struct class_device *classdev);