i915g: Don't write constants past I915_MAX_CONSTANT
i915g: Don't write constants past I915_MAX_CONSTANT

This happens with glsl-convolution-1, where we have 64 constants. This
doesn't make the test pass (we don't have 64 constants anyway, only
32) but this prevents it from crashing.

Signed-off-by: Stéphane Marchesin <e16f69845633a0cf74affe1e5a677caa6296c937@chromium.org>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler