As the unplug timer can potentially fire at any time, and and it access
data that is released by the md ->stop function, we need to del_timer_sync
before releasing that data.

(After much discussion, we created blk_sync_queue() for this)
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Contributions from Jens Axboe <axboe@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>