rcutorture: Small code cleanups

The rcu_torture_cleanup() function fails to NULL out the reader_tasks
pointer after freeing it and its fakewriter_tasks loop has redundant
braces.  This commit therefore cleans these up.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/rcu/rcutorture.c

@@ -2496,13 +2496,13 @@ rcu_torture_cleanup(void)
 			torture_stop_kthread(rcu_torture_reader,
 					     reader_tasks[i]);
 		kfree(reader_tasks);
+		reader_tasks = NULL;
 	}
 
 	if (fakewriter_tasks) {
-		for (i = 0; i < nfakewriters; i++) {
+		for (i = 0; i < nfakewriters; i++)
 			torture_stop_kthread(rcu_torture_fakewriter,
 					     fakewriter_tasks[i]);
-		}
 		kfree(fakewriter_tasks);
 		fakewriter_tasks = NULL;
 	}