mm: memory: use folio_throttle_swaprate() in wp_page_copy()

Directly use folio_throttle_swaprate() instead of
cgroup_throttle_swaprate().

Link: https://lkml.kernel.org/r/20230302115835.105364-5-wangkefeng.wang@huawei.com


Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>