DNSSEC: fix signer type in knot_is_valid_signature()

uint8_t * -> knot_dname_t *

refs #4

src/libknot/dnssec/rrset-sign.c

@@ -322,7 +322,7 @@ int knot_is_valid_signature(const knot_rrset_t *covered,
 	// identify fields in the signature being validated
 
 	uint8_t *rdata = knot_rrset_get_rdata(rrsigs, pos);
-	const uint8_t *signer = knot_rdata_rrsig_signer_name(rrsigs, pos);
+	const knot_dname_t *signer = knot_rdata_rrsig_signer_name(rrsigs, pos);
 
 	if (!rdata || !signer) {
 		return KNOT_EINVAL;