DVDInterface: Tweak speeds

The ratio between the speeds at the start and end needs to be equal to the ratio between the diameters of the start and end. Previously, I got these diameters by measuring discs with a ruler. The diameters defined in ECMA-267 are now used instead, resulting in a more accurate and slightly smaller ratio. (Previously part of the closed [PR 1617] (https://github.com/dolphin-emu/dolphin/pull/1617).)