Make mem_cgroup_inactive_anon_is_low return bool due to this particular
function only using either one or zero as its return value.

No functional change.
Signed-off-by: NYaowei Bai <bywxiaobai@163.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>