rcutorture: Fix missing-return bug in rcu_torture_barrier_init()

This commit adds a missing error return to the code path that creates
the rcu_torture_barrier() kthread.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

kernel/rcu/rcutorture.c

@@ -1245,6 +1245,7 @@ static int rcu_torture_barrier_init(void)
 		ret = PTR_ERR(barrier_task);
 		VERBOSE_TOROUT_ERRSTRING("Failed to create rcu_torture_barrier");
 		barrier_task = NULL;
+		return ret;
 	}
 	torture_shuffle_task_register(barrier_task);
 	return 0;