drm/nouveau/pm: several fixes for nvc0 memory timings

This patch fixes two small issues in timing generation as spotted on
several NVCx cards.

In addition, the header of the file is updated to also contain (some of)
the current developers of this code.

Signed-off-by: Roy Spliet <r.spliet@student.tudelft.nl>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>