mm/damon/vaddr: convert damon_young_pmd_entry() to use a folio

With damon_get_folio(), let's convert damon_young_pmd_entry()
to use a folio.

Link: https://lkml.kernel.org/r/20221230070849.63358-7-wangkefeng.wang@huawei.com


Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>