PixelShaderGen: Fix an issue with color combiner compare mode and simplify the affected line a bit.

This was a mistake of mine when translating floating point values to integer values.
Also, the max() part of that line was just completely redundant because the sign of an absolute value is always greater than or equal to zero.

Fixes issue 7178.
Merge pull request #276 from neobrain/master

PixelShaderGen: Color combiner compare mode fix and simplification