attribute_container: fix missing blank lines after declarations

Found with checkpatch.pl

Signed-off-by: Cosmin Dragomir <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/base/attribute_container.c

···
 attribute_container_unregister(struct attribute_container *cont)
 {
 	int retval = -EBUSY;
+
 	mutex_lock(&attribute_container_mutex);
 	spin_lock(&cont->containers.k_lock);
 	if (!list_empty(&cont->containers.k_list))
···
 attribute_container_add_class_device(struct device *classdev)
 {
 	int error = device_add(classdev);
+
 	if (error)
 		return error;
 	return attribute_container_add_attrs(classdev);