ubifs: Convert to filemap_migrate_folio()

filemap_migrate_folio() is a little more general than ubifs really needs,
but it's better to share the code.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

fs/ubifs/file.c

@@ -1461,29 +1461,6 @@ static bool ubifs_dirty_folio(struct address_space *mapping,
 	return ret;
 }
 
-#ifdef CONFIG_MIGRATION
-static int ubifs_migrate_page(struct address_space *mapping,
-		struct page *newpage, struct page *page, enum migrate_mode mode)
-{
-	int rc;
-
-	rc = migrate_page_move_mapping(mapping, newpage, page, 0);
-	if (rc != MIGRATEPAGE_SUCCESS)
-		return rc;
-
-	if (PagePrivate(page)) {
-		detach_page_private(page);
-		attach_page_private(newpage, (void *)1);
-	}
-
-	if (mode != MIGRATE_SYNC_NO_COPY)
-		migrate_page_copy(newpage, page);
-	else
-		migrate_page_states(newpage, page);
-	return MIGRATEPAGE_SUCCESS;
-}
-#endif
-
 static bool ubifs_release_folio(struct folio *folio, gfp_t unused_gfp_flags)
 {
 	struct inode *inode = folio->mapping->host;
@@ -1649,10 +1626,8 @@ const struct address_space_operations ubifs_file_address_operations = {
 	.write_end      = ubifs_write_end,
 	.invalidate_folio = ubifs_invalidate_folio,
 	.dirty_folio	= ubifs_dirty_folio,
-#ifdef CONFIG_MIGRATION
-	.migratepage	= ubifs_migrate_page,
-#endif
-	.release_folio    = ubifs_release_folio,
+	.migrate_folio	= filemap_migrate_folio,
+	.release_folio	= ubifs_release_folio,
 };
 
 const struct inode_operations ubifs_file_inode_operations = {