nvme-fc: fix numa_node when dev is null

A recent change added a numa_node field to the nvme controller
and has the transport assign the node using dev_to_node().
However, fcloop registers with a NULL device struct, so the
dev_to_node() call oops.

Revise the assignment to assign no node when device struct is null.

Fixes: 103e515e

 ("nvme: add a numa_node field to struct nvme_ctrl")
Reported-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Mike Snitzer <snitzer@redhat.com>
[hch: small coding style fixup]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>