nvme-fc: drop ctrl for all command completions

A requeue means we go through nvme_fc_start_fcp_op again and get
another controller reference.  To make sure the refcount doesn't
leak we also need to drop it for every completion that came from
the LLDD.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jens Axboe <axboe@fb.com>