dm: flakey fix corrupt_bio_byte error path

If no arguments were provided to the corrupt_bio_byte feature an error
should be returned immediately.

Reported-by: Zdenek Kabelac <zkabelac@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>