radeonsi: Better indexing of parameters in the pixel shader.

radeonsi: Better indexing of parameters in the pixel shader.

We were previously using the TGSI input index, which can exceed the number of
parameters passed from the vertex shader via the parameter cache. Now we use
a separate index which only counts those parameters.

Prevents piglit regressions with the following fix.

Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>