hwmon-vid: Don't spam the logs when VRM version is missing

If we cannot guess which VRM version the CPU uses, we set it to 0 and
log it. So we shouldn't spam the log each time vid_from_reg() is
later called with vrm 0.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Rudolf Marek <r.marek@assembler.cz>