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 v5.4.189 by commit 16fe77f86aa58418f20de13d614db88d608537bb, it was introduced in version v4.20 by commit 1bd54d851f50dea6af30c3e6ff4f3e9aab5558f9. For more details please see the references link.