nvme: don't pass the full CQE to nvme_complete_async_event

We only need the status and result fields, and passing them explicitly
makes life a lot easier for the Fibre Channel transport which doesn't
have a full CQE for the fast path case.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>