The voltage entries actually may map to a different voltage depending on
the current temperature.

v2: Only read the temperature when actually needed.
v5: Be smarter about using max().
    Don't read the temperature anymore.
Signed-off-by: NKarol Herbst <karolherbst@gmail.com>
Reviewed-by: NMartin Peres <martin.peres@free.fr>
Signed-off-by: NBen Skeggs <bskeggs@redhat.com>