blktrace: fix possible memory leak

When we failed to create "block" debugfs dir, we should do some
cleanups.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <49C2F5B2.8000800@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/blktrace.c

@@ -432,7 +432,7 @@ int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
 	if (!blk_tree_root) {
 		blk_tree_root = debugfs_create_dir("block", NULL);
 		if (!blk_tree_root)
-			return -ENOMEM;
+			goto err;
 	}
 
 	dir = debugfs_create_dir(buts->name, blk_tree_root);