r8169: use correct barrier between cacheable and non-cacheable memory

r8169 needs certain writes to be visible to other CPUs or the NIC before
touching the hardware, but was using smp_wmb() which is only required to
order cacheable memory access. Switch to wmb() which is required to
order both cacheable and non-cacheable memory.

Noticed by Catalin Marinas and Paul Mackerras.
Signed-off-by: David Dillow <dave@thedillows.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/r8169.c

@@ -4270,7 +4270,7 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
 
 	tp->cur_tx += frags + 1;
 
-	smp_wmb();
+	wmb();
 
 	RTL_W8(TxPoll, NPQ);	/* set polling bit */
 
@@ -4621,7 +4621,7 @@ static int rtl8169_poll(struct napi_struct *napi, int budget)
 		 * until it does.
 		 */
 		tp->intr_mask = 0xffff;
-		smp_wmb();
+		wmb();
 		RTL_W16(IntrMask, tp->intr_event);
 	}