drm/nvd7/therm: handle another kind of PWM fans

This should fix fan management on many nvd7+ chipsets.

Signed-off-by: Martin Peres <martin.peres@labri.fr>
Tested-by: Timothée Ravier <tim@siosm.fr>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>