tracing: add handler to trace_stat

Currently, if a trace_stat user wants a handle to some private data,
the trace_stat infrastructure does not supply a way to do that.

This patch passes the trace_stat structure to the start function of
the trace_stat code.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
diff --git a/kernel/trace/trace_workqueue.c b/kernel/trace/trace_workqueue.c
index 9ab035b..ee533c2 100644
--- a/kernel/trace/trace_workqueue.c
+++ b/kernel/trace/trace_workqueue.c
@@ -152,7 +152,7 @@
 	return ret;
 }
 
-static void *workqueue_stat_start(void)
+static void *workqueue_stat_start(struct tracer_stat *trace)
 {
 	int cpu;
 	void *ret = NULL;