udf: Convert empty_dir() to new directory iteration code

[ Upstream commit afb525f4 ]

Convert empty_dir() to new directory iteration code.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>