bt: controller/openisa: Use proper flexible array

0 length array is a GNU extension. Use proper C99 flexible
array.

Signed-off-by: Flavio Ceolin <[email protected]>

Author: ceolin

subsys/bluetooth/controller/ll_sw/openisa/lll/pdu_vendor.h

@@ -4,33 +4,27 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+#include <zephyr/sys/util.h>
+
 /* Minimum vendor specific Rx payload buffer allocation */
 #define LL_VND_OCTETS_RX_MIN 0
 
 /* No vendor Data PDU struct octet3 */
 struct pdu_data_vnd_octet3 {
-	union {
-		uint8_t resv[0];
-	} __packed;
+	FLEXIBLE_ARRAY_DECLARE(uint8_t, resv);
 } __packed;
 
 /* No vendor BIS PDU struct octet3 */
 struct pdu_bis_vnd_octet3 {
-	union {
-		uint8_t resv[0];
-	} __packed;
+	FLEXIBLE_ARRAY_DECLARE(uint8_t, resv);
 } __packed;
 
 /* No vendor CIS PDU struct octet3 */
 struct pdu_cis_vnd_octet3 {
-	union {
-		uint8_t resv[0];
-	} __packed;
+	FLEXIBLE_ARRAY_DECLARE(uint8_t, resv);
 } __packed;
 
 /* No ISOAL helper vendor ISO PDU struct octet3 */
 struct pdu_iso_vnd_octet3 {
-	union {
-		uint8_t resv[0];
-	} __packed;
+	FLEXIBLE_ARRAY_DECLARE(uint8_t, resv);
 } __packed;