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 v4.19.249 by commit 37ea1c1a2a813be27d62c6a13e0d9f35c2e5b0e6. For more details please see the references link.