nvme: keep ctrl->namespaces ordered

Various places in the nvme code that rely on ctrl->namespace to be
ordered.  Ensure that the namespae is inserted into the list at the
right position from the start instead of sorting it after the fact.

Fixes: 540c801c

 ("NVMe: Implement namespace list scanning")
Reported-by: Anton Eidelman <anton.eidelman@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>