nvme: properly handle partially initialized queues in nvme_create_io_queues

This avoids having to clean up later in a seemingly unrelated place.

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