powerpc/kasan: Silence KASAN warnings in _getwchan()
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 v5.15.49 by commit 70d6d6874db3cdead1ea31eb4656f01a0b40bd6a. For more details please see the references link.