kgdboc: fix return value of __setup handler
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 v4.9.311 by commit 1e7e9c5794bed0bc87c687d9496c83f1c389e7b4, it was introduced in version v4.9.137 by commit c90ea7d8b3109d2a09af1791908f0edd91bbe745. For more details please see the references link.