selftests/ftrace: Check set_event_pid result

Ensure the set_event_pid shows set pid list.
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>

tools/testing/selftests/ftrace/test.d/event/event-pid.tc

@@ -42,6 +42,7 @@ do_reset
 read mypid rest < /proc/self/stat
 
 echo $mypid > set_event_pid
+grep -q $mypid set_event_pid
 echo 'sched:sched_switch' > set_event
 
 yield