d3d8types.h: Convert the D3DVSD_...SHIFT constants to unsigned.

[Gerald Pfeifer]

On Mon, 26 Oct 2015, Henri Verbeet wrote:
> I don't think it really makes sense to make the shifts unsigned. There
> might be an argument for consistently using unsigned constants unless
> they need to be signed, but that would be a much larger change.

Okay.  If you want I could have a look, say converting one header
file, but I agree, it's not much of a priority.  Let me know in
case.

Gerald