EMI: Remove clamping from prepareTextures.

The intro looks fine to me with this set to false (it was changed in https://github.com/residualvm/residualvm/commit/4204b2649cb7e4572e168a993a619df4c3a0d2b0), but when it's set to true, it breaks things like the lava texture in the lava puzzle. This reverts the change and restores the lava texture.