It was already assuming a head page, so this is a straightforward
conversion.  Convert the one caller to call page_folio(), even though
it must currently be passing in a head page.
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NWilliam Kucharski <william.kucharski@oracle.com>