sysfs: fix kabi broken when add sysfs_emit and sysfs_emit_at

hulk inclusion
category: bugfix
bugzilla: NA
CVE: CVE-2021-27365

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It's introduced by 5bf67c8c2d947 ("sysfs: Add sysfs_emit and...").
Fix it by remove include mm.h.

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: zhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>