blk-mq: allow the callback to blk_mq_tag_busy_iter() to stop looping

blk-mq: allow the callback to blk_mq_tag_busy_iter() to stop looping

Currently blk_mq_tag_busy_iter() loops all busy tags for a given
hardware queue. But sometimes we are looking for a specific request,
and when we find it, we don't have to keep looking over the rest of
them. Change the busy_iter_fn callback to return a bool, where a
true return will break out of the search.

Update current callers (blk-mq timeout and NVMe IO cancel).

Signed-off-by: Jens Axboe <axboe@fb.com>