udf: fix retun value on error path in udf_load_logicalvol

In case we detect a problem and bail out, we fail to set "ret" to a
nonzero value, and udf_load_logicalvol will mistakenly report success.

Signed-off-by: Nikola Pajkovsky <npajkovs@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>