cleanup of deadline_dispatch_requests():

- replace drq selection with hopefully clearer while semantically the
  same construct: take write request, if there is any, otherwise take read
  one, or NULL if none exist.

- kill unused other_dir.
Signed-off-by: Nikita Danilov <nikita@clusterfs.com>
Cc: Jens Axboe <axboe@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>