blk-mq: blk_mq_tag_busy is no need to return a value

Currently "blk_mq_tag_busy" return value has no effect, so adjust it.
Some code implementations have also been adjusted to enhance
readability.

Signed-off-by: Liu Song <liusong@linux.alibaba.com>
Link: https://lore.kernel.org/r/1656170121-1619-1-git-send-email-liusong@linux.alibaba.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>