kernel/hung_task.c: change hung_task.c to use for_each_process_thread()

In check_hung_uninterruptible_tasks() avoid the use of deprecated
while_each_thread().

The "max_count" logic will prevent a livelock - see commit 0c740d0a
("introduce for_each_thread() to replace the buggy while_each_thread()").
Having said this let's use for_each_process_thread().

Signed-off-by: Aaron Tomlin <atomlin@redhat.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dave Wysochanski <dwysocha@redhat.com>
Cc: Aaron Tomlin <atomlin@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>