udf: fix udf_load_pvoldesc()

There are some missing braces here which means this function never
succeeds.

Fixes: e9d4cf41

 ('udf: improve error management in udf_CS0toUTF8()')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jan Kara <jack@suse.cz>