mm: vmscan: use sysfs_emit() to instead of scnprintf()

Replace open-coded snprintf() with sysfs_emit() to simplify the code.

Link: https://lkml.kernel.org/r/202211241929015476424@zte.com.cn


Signed-off-by: Xu Panda <xu.panda@zte.com.cn>
Signed-off-by: Yang Yang <yang.yang29@zte.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>