UBUNTU: SAUCE: fix compilation warning when CONFIG_SECURITY is not set

UBUNTU: SAUCE: fix compilation warning when CONFIG_SECURITY is not set

Function prototype differs when CONFIG_SECURITY is not set leading to
a warning:

include/linux/security.h: In function ‘security_task_free’:
include/linux/security.h:2244: warning: no return statement in function returning non-void

The patch that introduced this warning was Maverick commit:
  commit 2aec770a575b15cb1e43c2e16dff4f00a02a8c9a
  Author: Kees Cook <kees.cook@canonical.com>
  Date:   Mon Jun 28 22:34:04 2010 -0700

    UBUNTU: SAUCE: security: create task_free security callback

Acked-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Leann Ogasawara <leann.ogasawara@canonical.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@free.fr>