st: play it safe for now and check _NEW_PROGRAM for shader const buffer atom

When a new program is bound but no constants are updated we still need
to update the Gallium const buffer.

src/mesa/state_tracker/st_atom_constbuf.c

@@ -124,7 +124,7 @@ static void update_fs_constants(struct st_context *st )
 const struct st_tracked_state st_update_fs_constants = {
    "st_update_fs_constants",				/* name */
    {							/* dirty */
-      _NEW_PROGRAM_CONSTANTS,
+      (_NEW_PROGRAM | _NEW_PROGRAM_CONSTANTS),          /* mesa */
       ST_NEW_FRAGMENT_PROGRAM,				/* st */
    },
    update_fs_constants					/* update */