Remove state dependance from `stanncam_ratio_compensate_*` functions

[bfrymire]

The stanncam_ratio_compensate_* functions have the chance to return different values depending on the state of keeping the aspect ratio for STANNcam (stanncam_get_keep_aspect_ratio()).

The state dependence can be extracted from the function. and always return the correct ratio compensate value.

[stann-co]

.draw uses ratio compensate by default to ensure the game is drawn in the middle of the screen, if the aspect ratio doesn't match. And ratio_compensate changes depending on the actual ratio.