i2400m: remove some pointless conditionals before kfree_skb()

Remove some pointless conditionals before kfree_skb().
Signed-off-by: NWei Yongjun <yjwei@cn.fujitsu.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/wimax/i2400m/rx.c

@@ -177,8 +177,7 @@ void i2400m_rx_ctl_ack(struct i2400m *i2400m,
 	return;
 
 error_waiter_cancelled:
-	if (ack_skb)
-		kfree_skb(ack_skb);
+	kfree_skb(ack_skb);
 error_no_waiter:
 	spin_unlock_irqrestore(&i2400m->rx_lock, flags);
 	return;