tracing: Fix tracing_stat return values in error handling paths

tracing_stat_init() was always returning '0', even on the error paths.  It
now returns -ENODEV if tracing_init_dentry() fails or -ENOMEM if it fails
to created the 'trace_stat' debugfs directory.

Link: http://lkml.kernel.org/r/1410299381-20108-1-git-send-email-luis.henriques@canonical.com

Fixes: ed6f1c9 ("tracing: Check return value of tracing_init_dentry()")
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
[ Pulled from the archeological digging of my INBOX ]
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_stat.c

@@ -280,18 +280,22 @@ static int tracing_stat_init(void)
 
 	d_tracing = tracing_init_dentry();
 	if (IS_ERR(d_tracing))
-		return 0;
+		return -ENODEV;
 
 	stat_dir = tracefs_create_dir("trace_stat", d_tracing);
-	if (!stat_dir)
+	if (!stat_dir) {
 		pr_warn("Could not create tracefs 'trace_stat' entry\n");
+		return -ENOMEM;
+	}
 	return 0;
 }
 
 static int init_stat_file(struct stat_session *session)
 {
-	if (!stat_dir && tracing_stat_init())
-		return -ENODEV;
+	int ret;
+
+	if (!stat_dir && (ret = tracing_stat_init()))
+		return ret;
 
 	session->file = tracefs_create_file(session->ts->name, 0644,
 					    stat_dir,