fix(components): [el-cascader] placeholder disappeared after clear value

[sechi747]

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给el-cascader组件同时设置clearable和filterable属性后，点击清空按钮后placeholder没有正常显示
复现地址: here
gif演示

bug出现的原因是：#7540

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[github-actions]

🧪 Playground Preview: https://element-plus.run/?pr=9190
Please comment the example via this playground if needed.

[tolking]

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