mm: memcontrol: correct the comment of mem_cgroup_iter()

mm: memcontrol: correct the comment of mem_cgroup_iter()

Since commit bbec2e15170a ("mm: rename page_counter's count/limit into
usage/max"), the arg @reclaim has no priority field anymore.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Link: https://lkml.kernel.org/r/20200913094129.44558-1-linmiaohe@huawei.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>