reproducible arch: fix query for unknown results

Querying for 'UNKNOWN_%' will only return 0 results because LIKE treats
_ as a wildcard for exactly 1 character (while % would be 0, 1 or more)
but the status according to bin/reproducible_common.sh will be UNKNOWN

Signed-off-by: Holger Levsen <holger@layer-acht.org>