Duplicated aspect_ratio logic in phosphor-mask-calculations.fxh

[akgunter]

The function get_selected_aspect_ratio() in phosphor-mask-calculations.fxh has duplicated effort. I think I was comparing a switch statement to an if-else chain and forgot to delete one or the other. So now it's doing both. It doesn't cause any real problems, but I need to nuke one of them.