[Bug Report] Cascader 级联选择器 动态加载功能bug

### Element UI version
2.15.14

### OS/Browsers version
windows 11 / edge(119.0.2151.58)

### Vue version
2.6.14

### Reproduction Link
https://codepen.io/z-sq/pen/dyaJpPW

### Steps to reproduce
``` vue

export default {
data() {
return {
cascaderValue: [1,1,1],
props: {
lazy: true,
lazyLoad(node, resolve) {
const { level } = node;
if (level == 0) {
resolve([
{
value: 1,
label: `北京`,
leaf: false
}
]);
}else if (level == 1) {
resolve([
{
value: 1,
label: `北京`,
leaf: false
}
]);
}else if (level == 2) {
resolve([
{
value: 1,
label: `东城`,
leaf: true
}
]);
}
}
}
}
}
}
```

### What is Expected?
Cascader 级联选择器使用动态加载功能，级联数据的一二三级value一样，在回显时，选择的数据可以正常展示
北京/北京/东城区，id为【1,1,1】

### What is actually happening?
无法正常回显，再二级选项出现了4个一样的北京选项

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