Fix post comment add method

I've fixed method to work properly and avoid this issue:

```json
{
  "code": 500,
  "message": "An exception occurred while executing 'INSERT INTO news__comment (name, url, email, message, status, created_at, updated_at, post_id) VALUES (?, ?, ?, ?, ?, ?, ?, ?)' with params [\"grou\", \"http:\\/\\/sonata-project.org\", \"em@il.com\", \"grou\", null, \"2014-03-12 15:44:43\", \"2014-03-12 15:44:43\", null]:\n\nSQLSTATE[23000]: Integrity constraint violation: 1048 Column 'status' cannot be null"
}
```