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 v4.9.337 by commit 636a7013b8c08e43adaa86373c13f97b9b52f59b. For more details please see the references link.