drm/nouveau/bios/vpstate: There are some fermi vbios with no boost or tdp entry

If the entry size is too small, default to invalid values for both
boost_id and tdp_id, so as to default to the base clock in both cases.

Signed-off-by: Karol Herbst <karolherbst@gmail.com>
Signed-off-by: Martin Peres <martin.peres@free.fr>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>