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_stat.c b/kernel/trace/trace_stat.c
index f71b85b..f8f48d8 100644
--- a/kernel/trace/trace_stat.c
+++ b/kernel/trace/trace_stat.c
@@ -85,7 +85,7 @@
 	if (!ts->stat_cmp)
 		ts->stat_cmp = dummy_cmp;
 
-	stat = ts->stat_start();
+	stat = ts->stat_start(ts);
 	if (!stat)
 		goto exit;