[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: James Bottomley <James.Bottomley@SteelEye.com>
diff --git a/include/linux/attribute_container.h b/include/linux/attribute_container.h
index f54b05b..ee83fe6 100644
--- a/include/linux/attribute_container.h
+++ b/include/linux/attribute_container.h
@@ -64,6 +64,7 @@
 						 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);