secretmem: Convert to migrate_folio

This is little more than changing the types over; there's no real work
being done in this function.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

mm/secretmem.c

@@ -133,9 +133,8 @@ static const struct file_operations secretmem_fops = {
 	.mmap		= secretmem_mmap,
 };
 
-static int secretmem_migratepage(struct address_space *mapping,
-				 struct page *newpage, struct page *page,
-				 enum migrate_mode mode)
+static int secretmem_migrate_folio(struct address_space *mapping,
+		struct folio *dst, struct folio *src, enum migrate_mode mode)
 {
 	return -EBUSY;
 }
@@ -149,7 +148,7 @@ static void secretmem_free_folio(struct folio *folio)
 const struct address_space_operations secretmem_aops = {
 	.dirty_folio	= noop_dirty_folio,
 	.free_folio	= secretmem_free_folio,
-	.migratepage	= secretmem_migratepage,
+	.migrate_folio	= secretmem_migrate_folio,
 };
 
 static int secretmem_setattr(struct user_namespace *mnt_userns,