Add correct return type in order service

The method return $this. I corrected the doc-block.

Author: cmuench

app/code/Magento/Sales/Model/Service/OrderService.php

@@ -210,7 +210,7 @@ public function place(\Magento\Sales\Api\Data\OrderInterface $order)
      * @param string $comment
      * @param bool $isCustomerNotified
      * @param bool $shouldProtectState
-     * @return \Magento\Sales\Model\Order
+     * @return \Magento\Sales\Model\Service\OrderService
      * @throws \Magento\Framework\Exception\LocalizedException
      */
     public function setState(