percpu: fix a comment about the chunks ordering

mainline inclusion
from mainline-v5.14-rc1
commit ac9380f6
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4BE79


CVE: NA

-------------------------------------------------
Since the commit 3e54097b ("percpu: manage chunks based on
contig_bits instead of free_bytes") chunks are sorted based on the
size of the biggest continuous free area instead of the total number
of free bytes. Update the corresponding comment to reflect this.

Signed-off-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Dennis Zhou <dennis@kernel.org>
(cherry picked from commit ac9380f6)
Signed-off-by: Yuanzheng Song <songyuanzheng@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>