v3dv/pipeline: enable lower_add_sat NIR option

We don't support them by hw, so we would need to get them
lowered. This fix some crashes while using renderdoc with UE4 shooter
demo traces.
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <!8582>

src/broadcom/vulkan/v3dv_pipeline.c

@@ -205,6 +205,7 @@ static const struct spirv_to_nir_options default_spirv_options =  {
 };
 
 const nir_shader_compiler_options v3dv_nir_options = {
+   .lower_add_sat = true,
    .lower_all_io_to_temps = true,
    .lower_extract_byte = true,
    .lower_extract_word = true,