v3d/compiler: enable lower_add_sat NIR option

We are enabling this option for the Vulkan driver, so it makes sense
to enable it for the OpenGL one.
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Part-of: <!8582>

src/broadcom/compiler/nir_to_vir.c

@@ -3218,6 +3218,7 @@ nir_to_vir(struct v3d_compile *c)
 }
 
 const nir_shader_compiler_options v3d_nir_options = {
+        .lower_add_sat = true,
         .lower_all_io_to_temps = true,
         .lower_extract_byte = true,
         .lower_extract_word = true,