rcu: Fix rcu_torture_read ftrace event

Fix the rcutorturename field so that its size is correctly reported in
the text format embedded in trace.dat files. As it stands, it is
reported as being of size 1:

    field:char rcutorturename[8];   offset:8;       size:1; signed:0;

Signed-off-by: Douglas Raillard <[email protected]>
Reviewed-by: Mukesh Ojha <[email protected]>
Cc: [email protected]
Fixes: 04ae87a ("ftrace: Rework event_create_dir()")
Reviewed-by: Steven Rostedt (Google) <[email protected]>
[ boqun: Add "Cc" and "Fixes" tags per Steven ]
Signed-off-by: Boqun Feng <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>

Author: douglas-raillard-arm

include/trace/events/rcu.h

@@ -768,7 +768,7 @@ TRACE_EVENT_RCU(rcu_torture_read,
 	TP_ARGS(rcutorturename, rhp, secs, c_old, c),
 
 	TP_STRUCT__entry(
-		__field(char, rcutorturename[RCUTORTURENAME_LEN])
+		__array(char, rcutorturename, RCUTORTURENAME_LEN)
 		__field(struct rcu_head *, rhp)
 		__field(unsigned long, secs)
 		__field(unsigned long, c_old)