kmemtrace: add kmemtrace_init()

Impact: build fix

leftover from the relayfs version - but we want to keep it because
this call is the earliest opportunity when we can start kmemtrace
tracing. (after kmem_cache_init()).
Signed-off-by: NIngo Molnar <mingo@elte.hu>

kernel/trace/kmemtrace.c

@@ -337,6 +337,11 @@ static struct tracer kmem_tracer __read_mostly = {
 	.flags		= &kmem_tracer_flags
 };
 
+void kmemtrace_init(void)
+{
+	/* earliest opportunity to start kmem tracing */
+}
+
 static int __init init_kmem_tracer(void)
 {
 	return register_tracer(&kmem_tracer);