fix lint

Signed-off-by: yisaer <disxiaofei@163.com>

planner/core/rule_join_reorder.go

@@ -252,11 +252,13 @@ func extractJoinAndDataSource(t *tracing.LogicalPlanTrace) *tracing.LogicalPlanT
 	return root
 }
 
+// simplify only keeps Proj and DataSource operators, and discard other operators.
 func simplify(node *tracing.LogicalPlanTrace) {
 	if len(node.Children) < 1 {
 		return
 	}
-	for valid := true; !valid; valid = true {
+	for valid := true; !valid; {
+		valid = true
 		newChildren := make([]*tracing.LogicalPlanTrace, 0)
 		for _, child := range node.Children {
 			if child.TP != plancodec.TypeDataSource && child.TP != plancodec.TypeJoin {