cycles separateRGB: fix for cuda kernel building. Array indexing doesn't work there.
cycles separateRGB: fix for cuda kernel building.
Array indexing doesn't work there.

I'm yet to setup my CUDA computer, in the meantime this proved to work (tested by Daniel Salazar).
If I found other ways of doing it I get back to that.

pyrochlore/cycles,pyrochlore/cycles,pyrochlore/cycles,tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird