nfs: Convert to free_folio

Add a wrapper that converts back from the folio to the page.  This
entire file needs to be converted to use folios, but that's a
task for a different set of patches.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

fs/nfs/dir.c

@@ -55,7 +55,7 @@ static int nfs_closedir(struct inode *, struct file *);
 static int nfs_readdir(struct file *, struct dir_context *);
 static int nfs_fsync_dir(struct file *, loff_t, loff_t, int);
 static loff_t nfs_llseek_dir(struct file *, loff_t, int);
-static void nfs_readdir_clear_array(struct page*);
+static void nfs_readdir_free_folio(struct folio *);
 
 const struct file_operations nfs_dir_operations = {
 	.llseek		= nfs_llseek_dir,
@@ -67,7 +67,7 @@ const struct file_operations nfs_dir_operations = {
 };
 
 const struct address_space_operations nfs_dir_aops = {
-	.freepage = nfs_readdir_clear_array,
+	.free_folio = nfs_readdir_free_folio,
 };
 
 #define NFS_INIT_DTSIZE PAGE_SIZE
@@ -228,6 +228,11 @@ static void nfs_readdir_clear_array(struct page *page)
 	kunmap_atomic(array);
 }
 
+static void nfs_readdir_free_folio(struct folio *folio)
+{
+	nfs_readdir_clear_array(&folio->page);
+}
+
 static void nfs_readdir_page_reinit_array(struct page *page, u64 last_cookie,
 					  u64 change_attr)
 {