Magento 2 : Adding multiple configurable product variations in cart

I have got answer, issue is product object override next loop, in controller,

we have to create each time new product object and now its working after doing below changes.

Instead of $product = $this->initProduct($params['product']);we have set below line,

$storeId = $this->_objectManager->get('Magento\Store\Model\StoreManagerInterface')->getStore()->getId();
$product = $this->_objectManager->create('Magento\Catalog\Model\Product')->setStoreId($storeId)->load($params['product']);

Its works.