Update field 540

Fix field 540 to use the current notation. Based on MELKEHITYS-2431. Example:

540 ## $c CC BY 4.0 $u https://creativecommons.org/licenses/by/4.0/deed.fi → 540 ## $f CC BY 4.0 $2 cc $u https://creativecommons.org/licenses/by/4.0/deed.fi