s390/decompressor: specify __decompress() buf len to avoid overflow
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 v5.15.95 by commit 9ed522143f959630f8b7782ddc212900d8f609a9. For more details please see the references link.