bootstd: Indicate refresh need with bootflow_menu_poll()

When the user presses 'up' when on the top menu item, it is a waste of
time to refresh since nothing has changed.

Add a new return code from this function to indicate that the UI must be
refreshed.

Signed-off-by: Simon Glass <sjg@chromium.org>

boot/bootflow_menu.c

@@ -309,6 +309,8 @@ int bootflow_menu_poll(struct expo *exp, int *seqp)
 		ret = scene_menu_select_item(scn, OBJ_MENU, act.select.id);
 		if (ret)
 			return log_msg_ret("bmp", ret);
+		if (act.select.changed)
+			return -EREMCHG;
 		return -ERESTART;
 	}
 	case EXPOACT_QUIT: