crypto/null: use ring size function

Rather than reading the size directly from the ring structure,
use the dedicated function for that purpose.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Declan Doherty <declan.doherty@intel.com>

drivers/crypto/null/null_crypto_pmd_ops.c

@@ -193,7 +193,7 @@ null_crypto_pmd_qp_create_processed_pkts_ring(struct null_crypto_qp *qp,
 
 	r = rte_ring_lookup(qp->name);
 	if (r) {
-		if (r->prod.size >= ring_size) {
+		if (rte_ring_get_size(r) >= ring_size) {
 			NULL_CRYPTO_LOG_INFO(
 				"Reusing existing ring %s for processed packets",
 				qp->name);