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

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

src/mesa/state_tracker/st_atom_shader.c

@@ -60,7 +60,8 @@ get_passthrough_fs(struct st_context *st)
    if (!st->passthrough_fs) {
       st->passthrough_fs =
          util_make_fragment_passthrough_shader(st->pipe, TGSI_SEMANTIC_COLOR,
-                                               TGSI_INTERPOLATE_PERSPECTIVE);
+                                               TGSI_INTERPOLATE_PERSPECTIVE,
+                                               TRUE);
    }
 
    return st->passthrough_fs;