nvme: don't rely on the changed namespace list log

Don't optimize our namespace rescan based on the changed namespace list
log page as userspace might have changed the content through reading
it.

Suggested-by: Keith Busch <keith.busch@linux.intel.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <keith.busch@linux.intel.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>