ethoc: fix typo to compute number of tx descriptors

It should be max() instead of min(). Use 1/4 of available
descriptors for tx, and there should be at least 2 tx
descriptors.
Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethoc.c

@@ -655,7 +655,7 @@ static int ethoc_open(struct net_device *dev)
 
 	/* calculate the number of TX/RX buffers */
 	num_bd = (dev->mem_end - dev->mem_start + 1) / ETHOC_BUFSIZ;
-	priv->num_tx = min(min_tx, num_bd / 4);
+	priv->num_tx = max(min_tx, num_bd / 4);
 	priv->num_rx = num_bd - priv->num_tx;
 	ethoc_write(priv, TX_BD_NUM, priv->num_tx);