blk-mq: use blk_mq_commit_rqs helper in blk_mq_try_issue_list_directly

Call blk_mq_commit_rqs instead of access ->commit_rqs directly. As you
can see in comment of blk_mq_commit_rqs, we only need explicitly call
this in two cases:
 -did not queue everything initially scheduled to queue
 -the last attempt to queue a request failed
Both cases can be checked with ret of last request which breaks list
walk. Then we can remove unnecessary error count and unnecessary
commit triggered by error besides cases described above.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>