nvc0: avoid tex read fault from compute shaders on GK110

nvc0: avoid tex read fault from compute shaders on GK110

After some investigation, it seems like that disabling the UNK02C4
command avoid a read fault with texelFetch() from a compute shader.

I have no clue on what this method actually does, but this avoid the
GPU to hang with basic-texelFetch.shader_test without introducing any
compute-related regressions.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Acked-by: Ilia Mirkin <imirkin@alum.mit.edu>