perf/core: Make perf_swevent_init_cpu() static

'make W=1' causes GCC to complain:

  kernel/events/core.c:11877:6: warning: no previous prototype for 'perf_swevent_init_cpu' [-Wmissing-prototypes]

It's not referenced anywhere else, make it static.

Signed-off-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/28974.1552377997@turing-police
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 72d06e30..dfc4bab 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -11878,7 +11878,7 @@ static void __init perf_event_init_all_cpus(void)
 	}
 }
 
-void perf_swevent_init_cpu(unsigned int cpu)
+static void perf_swevent_init_cpu(unsigned int cpu)
 {
 	struct swevent_htable *swhash = &per_cpu(swevent_htable, cpu);