r300/compiler: Fix bug when lowering KILP on r300 cards

r300/compiler: Fix bug when lowering KILP on r300 cards

KILP instruction inside IF blocks were being lowered to an unconditional
KIL.  Since r300 doesn't support branching, when the IF's were lowered
to conditional moves, the KIL would always be executed.  This is not a
problem with the mesa state tracker, because the GLSL compiler handles
lowering IF's, but this bug was appearing in the VDPAU state tracker,
which does not use the GLSL compiler.

Note: This is a candidate for the stable branches.