net: ethernet: dnet: Remove set but unused variable 'len'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/net/ethernet/dnet.c: In function dnet_start_xmit
drivers/net/ethernet/dnet.c:511:15: warning: variable ‘len’ set but not used [-Wunused-but-set-variable]

commit 47964174 ("dnet: Dave DNET ethernet controller driver (updated)")
involved this unused variable, remove it.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wang Hai <wanghai38@huawei.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/dnet.c

@@ -508,7 +508,7 @@ static netdev_tx_t dnet_start_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	struct dnet *bp = netdev_priv(dev);
 	u32 tx_status, irq_enable;
-	unsigned int len, i, tx_cmd, wrsz;
+	unsigned int i, tx_cmd, wrsz;
 	unsigned long flags;
 	unsigned int *bufp;
 
@@ -518,9 +518,6 @@ static netdev_tx_t dnet_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	       skb->len, skb->head, skb->data);
 	dnet_print_skb(skb);
 
-	/* frame size (words) */
-	len = (skb->len + 3) >> 2;
-
 	spin_lock_irqsave(&bp->lock, flags);
 
 	tx_status = dnet_readl(bp, TX_STATUS);