nvme-fabrics: handle the admin-only case properly in nvmf_check_ready

In the ADMIN_ONLY state we don't have any I/O queues, but we should accept
all admin commands without further checks.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by:  James Smart <james.smart@broadcom.com>