[GLES] Fix for SBS rendering and cached viewport

I've also changed the unused function CLinuxRendererGLES::RenderMultiPass
to use the caching wrapper for SetViewPort.
Makes no odds now, but may avoid a problem if it's enabled in future.
Merge pull request #3754 from popcornmix/fix_viewport_cache

[GLES] Fix for SBS rendering and cached viewport