ibmveth: Use lighter weight read memory barrier in ibmveth_poll

We want to order the read in ibmveth_rxq_pending_buffer and the read of
ibmveth_rxq_buffer_valid which are both cacheable memory. smp_rmb() is good
enough for this.
Signed-off-by: NAnton Blanchard <anton@samba.org>
Signed-off-by: NSantiago Leon <santil@linux.vnet.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ibmveth.c

@@ -1010,7 +1010,7 @@ static int ibmveth_poll(struct napi_struct *napi, int budget)
 		if (!ibmveth_rxq_pending_buffer(adapter))
 			break;
 
-		rmb();
+		smp_rmb();
 		if (!ibmveth_rxq_buffer_valid(adapter)) {
 			wmb(); /* suggested by larson1 */
 			adapter->rx_invalid_buffer++;