nvme: register ns_id attributes as default sysfs groups

We should be registering the ns_id attribute as default sysfs
attribute groups, otherwise we have a race condition between
the uevent and the attributes appearing in sysfs.

Suggested-by: Bart van Assche <bvanassche@acm.org>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>