perf: Make __perf_event_sched_out static

__perf_event_sched_out doesn't need to be globally available, make
it static.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>

kernel/perf_event.c

@@ -1049,8 +1049,8 @@ static int perf_event_refresh(struct perf_event *event, int refresh)
 	return 0;
 }
 
-void __perf_event_sched_out(struct perf_event_context *ctx,
-			      struct perf_cpu_context *cpuctx)
+static void __perf_event_sched_out(struct perf_event_context *ctx,
+				   struct perf_cpu_context *cpuctx)
 {
 	struct perf_event *event;