trace: fix logic to start/stop counting

The logic in the tracing_start/stop code prevents the WARN_ON
from ever detecting if a start/stop pair was mismatched.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/trace.c

@@ -610,13 +610,12 @@ void tracing_start(void)
 		return;
 
 	spin_lock_irqsave(&tracing_start_lock, flags);
-	if (--trace_stop_count)
-		goto out;
-
+	if (--trace_stop_count) {
 		if (trace_stop_count < 0) {
 			/* Someone screwed up their debugging */
 			WARN_ON_ONCE(1);
 			trace_stop_count = 0;
+		}
 		goto out;
 	}