udf: simple cleanup of truncate.c

- remove one indentation level by little code reorganization
- convert "if (smth) BUG();" to "BUG_ON(smth);"

Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
1 file changed