mm/memcontrol.c: fix parameter description mismatch

mm/memcontrol.c: fix parameter description mismatch

There are a couple of places where parameter description and function
name do not match the actual code.  Fix it.

Link: http://lkml.kernel.org/r/1520843448-17347-1-git-send-email-honglei.wang@oracle.com
Signed-off-by: Honglei Wang <honglei.wang@oracle.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>