Based on the Hardware Ids the device is a "Realtek PCIE Card Reader":
http://www.pcidatabase.com/search.php?device_search_str=5289&device_search=Search
ASUS appears to have a driver available for Windows 8 under "Card Reader" for the K55A:
http://support.asus.com/Download.aspx?SLanguage=en&m=K55A&p=3&s=386