udf: Convert udf_lookup() to use new directory iteration code

[ Upstream commit 200918b3 ]

Convert udf_lookup() to use udf_fiiter_find_entry() for looking up
directory entries.

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>