Documentation: cgroup: Fix 'cgroup-legacy' -> 'cgroup-v1'

This should have happened in 6255c46f (cgroup: rename cgroup
documentations, 2016-01-11).

Signed-off-by: W. Trevor King <wking@tremily.us>
Signed-off-by: Tejun Heo <tj@kernel.org>
1 file changed