drm/nouveau/bios/volt: Parse min and max for Version 0x40

This is according to what we have in nvbios.

Fixes "ERROR: Can't get value of subfeature in0_min: Can't read" errors
in sensors for some GPUs.

Signed-off-by: Karol Herbst <karolherbst@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>