mm: convert soft_offline_in_use_page() to use a folio

Replace the existing head-page logic with folio logic.

Link: https://lkml.kernel.org/r/20231108182809.602073-5-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>