[965] Fix negating of unsigned value in emit_wpos_xy.

src/mesa/drivers/dri/i965/brw_wm_emit.c

@@ -137,7 +137,7 @@ static void emit_wpos_xy(struct brw_wm_compile *c,
       brw_ADD(p,
 	      dst[0],
 	      retype(arg0[0], BRW_REGISTER_TYPE_W),
-	      brw_imm_d(- c->key.origin_x));
+	      brw_imm_d(0 - c->key.origin_x));
    }
 
    if (mask & WRITEMASK_Y) {