fs: Convert __page_get_link() to use a folio

Retrieve a folio from the page cache instead of a page and operate
on it.  Removes two hidden calls to compound_head().

Signed-off-by: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Link: https://lore.kernel.org/20250514171316.3002934-2-willy@infradead.org


Signed-off-by: Christian Brauner <brauner@kernel.org>