procps: whitelist CVE-2018-1121

This CVE is about race conditions in 'ps' which make it unsuitable for security
audits.  As these race conditions are unavoidable ps shouldn't be used for
security auditing, so this isn't a valid CVE.

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Anuj Mittal <anuj.mittal@intel.com>