st_glsl_to_tgsi: use calloc the way it's meant to be used
st_glsl_to_tgsi: use calloc the way it's meant to be used

Reviewed-by: Marek Olšák <8c7344a1abdb103e79ecfd488098373070c3c70e@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler