mm/swapfile.c: fix a comment in sys_swapon()

mainline inclusion
from mainline-5.6-rc3
commit fed98ef4
category: bugfix
bugzilla: 50612
CVE: NA
---------------------------

claim_swapfile now always takes i_rwsem.

Link: http://lkml.kernel.org/r/20200114161225.309792-2-hch@lst.de


Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>
Reviewed-by: Yang Erkun <yangerkun@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>