nvme_fc: fix double calls to nvme_cleanup_cmd()

Current fc transport code, on io termination, is calling
nvme_cleanup_cmd() followed by the transport dma unmap routine
which also calls nvme_cleanup_cmd(). Which means two kfrees occur
on the same address, raising havoc. This resulted in odd data errors,
effectively corruption..

Fix by removing the extraneous double calls. Call now occurs only in
teardown paths and as part of dma unmap routine.

Signed-off-by: James Smart <james.smart@broadcom.com>
Reviewed-by: Ewan D. Milne <emilne@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>