softlockup: Fix hung_task_check_count sysctl

I'm seeing spikes of up to 0.5ms in khungtaskd on a large
machine. To reduce this source of jitter I tried setting
hung_task_check_count to 0:

 # echo 0 > /proc/sys/kernel/hung_task_check_count

which didn't have the intended response. Change to a post
increment of max_count, so a value of 0 means check 0 tasks.
Signed-off-by: Anton Blanchard <anton@samba.org>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: msb@google.com
LKML-Reference: <20091127022820.GU32182@kryten>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/hung_task.c

@@ -144,7 +144,7 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
 
 	rcu_read_lock();
 	do_each_thread(g, t) {
-		if (!--max_count)
+		if (!max_count--)
 			goto unlock;
 		if (!--batch_count) {
 			batch_count = HUNG_TASK_BATCHING;