r300: Fix fogcoord rewriting

r300: Fix fogcoord rewriting

We only care about the actual fogcoord itself now, reducing the rewriting
done for the vertex program.

The rewriting of source operand swizzles in the fragment program takes
care that fogcoord.yzw = 001.

This should fix fogcoord rewriting entirely, which had been horribly
broken in the face of dot-product instructions, and just broken (though
not horribly so) in the face of almost every other instruction (the W
component would be incorrect for most arithmetic instructions).

Signed-off-by: Nicolai Hähnle <nhaehnle@gmail.com>