tracing: initialize return value for __ftrace_set_clr_event

Commit 8f31bfe538ebafac187d2d4465a92e1d9ee6d8c2
tracing/events: clean up for ftrace_set_clr_event()

Moved out the code for ftrace_set_clr_event into a helper funciton but
did not initialize the return value. As a result, we do not warn about
a typo in the echoing of events in set_event.

This patch restores the old warning:

 # echo foobar > set_event
-bash: echo: write error: Invalid argument

[ Impact: restore warning of invalid entries to set_event ]

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace_events.c

@@ -118,7 +118,7 @@ static int __ftrace_set_clr_event(const char *match, const char *sub,
 				  const char *event, int set)
 {
 	struct ftrace_event_call *call;
-	int ret;
+	int ret = -EINVAL;
 
 	mutex_lock(&event_mutex);
 	list_for_each_entry(call, &ftrace_events, list) {