Pull cgroup updates from Tejun Heo:
"Nothing too interesting. Documentation updates and trivial changes;
however, this pull request does containt he previusly discussed
dropping of __must_check from strscpy()"
* 'for-4.16' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
Documentation: Fix 'file_mapped' -> 'mapped_file'
string: drop __must_check from strscpy() and restore strscpy() usages in cgroup
cgroup, docs: document the root cgroup behavior of cpu and io controllers
cgroup-v2.txt: fix typos
cgroup: Update documentation reference
Documentation/cgroup-v1: fix outdated programming details
cgroup, docs: document cgroup v2 device controller