tools/vm/page_owner_sort.c: fix the instructions for use

tools/vm/page_owner_sort.c: fix the instructions for use

I noticed a discrepancy between the usage method and the code logic.

If we enable the -f option, it should be "Filter out the information of
blocks whose memory has been released".

Link: https://lkml.kernel.org/r/20220219143106.2805-1-caoyixuan2019@email.szu.edu.cn
Signed-off-by: Yixuan Cao <caoyixuan2019@email.szu.edu.cn>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Sean Anderson <seanga2@gmail.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Zhenliang Wei <weizhenliang@huawei.com>
Cc: Tang Bin <tangbin@cmss.chinamobile.com>
Cc: Yinan Zhang <zhangyinan2019@email.szu.edu.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>