cgroup/cpuset: Remove unneeded goto in sched_partition_write() and rename it

The goto statement in sched_partition_write() is not needed. Remove
it and rename sched_partition_write()/sched_partition_show() to
cpuset_partition_write()/cpuset_partition_show().

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>