rcu: Convert ACCESS_ONCE() to READ_ONCE() and WRITE_ONCE()

This commit moves from the old ACCESS_ONCE() API to the new READ_ONCE()
and WRITE_ONCE() APIs.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck:  Updated to include kernel/torture.c as suggested by Jason Low. ]

kernel/rcu/rcutorture.c

@@ -1413,7 +1413,7 @@ static int rcu_torture_barrier_cbs(void *arg)
 	do {
 		wait_event(barrier_cbs_wq[myid],
 			   (newphase =
-			    ACCESS_ONCE(barrier_phase)) != lastphase ||
+			    READ_ONCE(barrier_phase)) != lastphase ||
 			   torture_must_stop());
 		lastphase = newphase;
 		smp_mb(); /* ensure barrier_phase load before ->call(). */