mm/page_alloc: correct the wrong cpuset file path in comment

cpuset.c was moved to kernel/cgroup/ in below commit
201af4c0 ("cgroup: move cgroup files under kernel/cgroup/")
Correct the wrong path in comment.

Link: https://lkml.kernel.org/r/20220718120336.5145-1-mark-pk.tsai@mediatek.com


Signed-off-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>