mm: madvise: use vm_normal_folio() in madvise_free_pte_range()

There is already a vm_normal_folio(), use it to make
madvise_free_pte_range() only use a folio.

Link: https://lkml.kernel.org/r/20230112124028.16964-1-wangkefeng.wang@huawei.com


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