nvme: count all ANA groups for ANA Log page

When issuing a short read on the ANA log page the number of groups
should not change, even though the final returned data might contain
less groups than that number.

Signed-off-by: Hannes Reinecke <hare@suse.com>
[switched to a for loop]
Signed-off-by: Christoph Hellwig <hch@lst.de>