kernel/audit_tree.c: tree will leak memory when failure occurs in audit_trim_trees()

audit_trim_trees() calls get_tree(). If a failure occurs we must call
put_tree().

[[e-mail]: run put_tree() before mutex_lock() for small scalability improvement]
Signed-off-by: Chen Gang <[e-mail]>
Cc: Al Viro <[e-mail]>
Cc: Eric Paris <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

kernel/audit_tree.c

···
 		}
 		spin_unlock(&hash_lock);
 		trim_marked(tree);
-		put_tree(tree);
 		drop_collected_mounts(root_mnt);
 skip_it:
+		put_tree(tree);
 		mutex_lock(&audit_filter_mutex);
 	}
 	list_del(&cursor);