examples/suit_update/tests: use current version as invalid one
examples/suit_update/tests: use current version as invalid one

If the current version was 0 then previously an invalid <0 seq_no
would be used.

OlegHahm/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,miri64/RIOT,kYc0o/RIOT,kYc0o/RIOT,jasonatran/RIOT,OlegHahm/RIOT,ant9000/RIOT,jasonatran/RIOT,OlegHahm/RIOT,kaspar030/RIOT,kYc0o/RIOT,OlegHahm/RIOT,miri64/RIOT,OlegHahm/RIOT,miri64/RIOT,kaspar030/RIOT,miri64/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,ant9000/RIOT,miri64/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,kaspar030/RIOT,ant9000/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,ant9000/RIOT,jasonatran/RIOT,ant9000/RIOT