nvmet: call blk_mq_free_request() directly

Instead of calling blk_put_request() which calls blk_mq_free_request(),
call blk_mq_free_request() directly for NVMeOF passthru. This is to
mainly avoid an extra function call in the completion path
nvmet_passthru_req_done().

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>