pid: take a reference when initializing cad_pid
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 v4.4.272 by commit 764c2e892d1fe895392aff62fb353fdce43bb529, it was introduced in version v2.6.19 by commit 9ec52099e4b8678a60e9f93e41ad87885d64f3e6. For more details please see the references link.