sfc: don't call tx_remove if there isn't one

EF100 won't have an efx->type->tx_remove method, because there's
 nothing for it to do.  So make the call conditional.
Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/sfc/nic_common.h

@@ -163,7 +163,8 @@ static inline void efx_nic_init_tx(struct efx_tx_queue *tx_queue)
 }
 static inline void efx_nic_remove_tx(struct efx_tx_queue *tx_queue)
 {
-	tx_queue->efx->type->tx_remove(tx_queue);
+	if (tx_queue->efx->type->tx_remove)
+		tx_queue->efx->type->tx_remove(tx_queue);
 }
 static inline void efx_nic_push_buffers(struct efx_tx_queue *tx_queue)
 {