Get_mcn(kdev_t dev, struct cdrom_mcn*mcn)

Some discs carry a `Media Catalog Number' (MCN), also called `Universal Product Code' (UPC). This number should reflect the number that is generally found in the bar-code on the product. Unfortunately, the few discs that carry such a number on the disc don't even use the same format. The return argument to this function is a pointer to a pre-declared memory region of type struct cdrom_mcn. The MCN is expected as a 13-character string, terminated by a null-character.