blk-mq: do not reset plug->rq_count before the list is sorted

blk-mq: do not reset plug->rq_count before the list is sorted

[ Upstream commit bcc816dfe51ab86ca94663c7b225f2d6eb0fddb9 ]

We would never be able to sort the list if we first reset plug->rq_count
which is used in conditional check later.

Fixes: ce5b009cff19 ("block: improve logic around when to sort a plug list")
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin (Microsoft) <sashal@kernel.org>