gallium/util: make WRITES_ALL_CBUFS optional in the passthrough fragment shader

Reviewed-by: Brian Paul <brianp@vmware.com>

src/gallium/state_trackers/vega/renderer.c

@@ -309,7 +309,8 @@ static void renderer_set_fs(struct renderer *r, RendererFs id)
       switch (id) {
       case RENDERER_FS_COLOR:
          fs = util_make_fragment_passthrough_shader(r->pipe,
-                          TGSI_SEMANTIC_COLOR, TGSI_INTERPOLATE_PERSPECTIVE);
+                          TGSI_SEMANTIC_COLOR, TGSI_INTERPOLATE_PERSPECTIVE,
+                          TRUE);
          break;
       case RENDERER_FS_TEXTURE:
          fs = util_make_fragment_tex_shader(r->pipe,