tracing: Mark tracing_dentry_percpu() static

Nothing outside of kernel/trace/trace.c references tracing_dentry_percpu().

Link: http://lkml.kernel.org/r/1353302917-13995-7-git-send-email-josh@joshtriplett.org

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -4506,7 +4506,7 @@ struct dentry *tracing_init_dentry(void)
 
 static struct dentry *d_percpu;
 
-struct dentry *tracing_dentry_percpu(void)
+static struct dentry *tracing_dentry_percpu(void)
 {
 	static int once;
 	struct dentry *d_tracer;