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: NJames Morris <james.l.morris@oracle.com>

MAINTAINERS

@@ -7948,6 +7948,7 @@ F:	drivers/mmc/host/sdhci-spear.c
 
 SECURITY SUBSYSTEM
 M:	James Morris <james.l.morris@oracle.com>
+M:	Serge E. Hallyn <serge@hallyn.com>
 L:	linux-security-module@vger.kernel.org (suggested Cc:)
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security.git
 W:	http://kernsec.org/