security: add Serge Hallyn as a maintainer

Add Serge E. Hallyn <serge@hallyn.com> as a co-maintainer of the
security subsystem, to avoid having a single point of failure
in the development process.

Signed-off-by: James Morris <james.l.morris@oracle.com>
Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security

Pull security maintainership update from James Morris:
 "Add Serge Hallyn as security subsystem co-maintainer"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security:
  security: add Serge Hallyn as a maintainer