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 v5.15.86 by commit 8131d1880c094e1d9c320320350f0b7127e2e876. For more details please see the references link.