Use integer-casted argument in Cursor::batchSize()

lib/Doctrine/MongoDB/Cursor.php

@@ -113,7 +113,7 @@ public function addOption($key, $value)
      */
     public function batchSize($num)
     {
-        $limit = (integer) $num;
+        $num = (integer) $num;
         $this->batchSize = $num;
         $this->mongoCursor->batchSize($num);
         return $this;