s390/ctcm: Fix return type of ctc{mp,}m_tx()
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v5.10.163 by commit eeb75f80bceb88091722611b694042879aea1231. For more details please see the references link.