Fix build warning in kernel/cpuset.c

Fix build warning in kernel/cpuset.c

BugLink: http://bugs.launchpad.net/bugs/1629386
>           2 ../kernel/cpuset.c:2101:11: warning: initialization from incompatible pointer type [-Wincompatible-pointer-types]
>           1 ../kernel/cpuset.c:2101:2: warning: initialization from incompatible pointer type
>           1 ../kernel/cpuset.c:2101:2: warning: (near initialization for 'cpuset_cgrp_subsys.fork')

This got introduced by 06ec7a1d7646 ("cpuset: make sure new tasks
conform to the current config of the cpuset"). In the upstream
kernel, the function prototype was changed as of b53202e63089
("cgroup: kill cgrp_ss_priv[CGROUP_CANFORK_COUNT] and friends").

That patch is not suitable for stable kernels, and fortunately
the warning seems harmless as the prototypes only differ in the
second argument that is unused. Adding that argument gets rid
of the warning:

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>