drm/amd/powerplay: correct data type to support under voltage

For under voltage, negative value will be applied to voltage
offset. Update the data type to cover this case.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
1 file changed