rsx: Clamp negative fog distance

[kd-11]

• Noticed while looking through ngs1 traces that the fog distance was negative due to (scale * coord) being less than the bias variable (equation is generally scale * coord + bias and bias can be negative with some equations). Opened as a separate PR to make testing easier.

[IbanPetrov]

Thanks very much for ninja gaiden

[kingxicefire]

thank you for your hard work kd-11.