Prevent build warning when CONFIG_FUNCTION_GRAPH_TRACER is not set.
Signed-off-by: NLai Jiangshan <laijs@cn.fujitsu.com>
LKML-Reference: <4AF24381.5060307@cn.fujitsu.com>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>