drivers/net: eliminate irq handler impossible checks, needless casts

- Eliminate check for irq handler 'dev_id==NULL' where the
  condition never occurs.

- Eliminate needless casts to/from void*

Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/drivers/net/wireless/wl3501_cs.c b/drivers/net/wireless/wl3501_cs.c
index a143035..5b98a78 100644
--- a/drivers/net/wireless/wl3501_cs.c
+++ b/drivers/net/wireless/wl3501_cs.c
@@ -1155,25 +1155,18 @@
  */
 static irqreturn_t wl3501_interrupt(int irq, void *dev_id)
 {
-	struct net_device *dev = (struct net_device *)dev_id;
+	struct net_device *dev = dev_id;
 	struct wl3501_card *this;
-	int handled = 1;
 
-	if (!dev)
-		goto unknown;
-	this = dev->priv;
+	this = netdev_priv(dev);
 	spin_lock(&this->lock);
 	wl3501_ack_interrupt(this);
 	wl3501_block_interrupt(this);
 	wl3501_rx_interrupt(dev);
 	wl3501_unblock_interrupt(this);
 	spin_unlock(&this->lock);
-out:
-	return IRQ_RETVAL(handled);
-unknown:
-	handled = 0;
-	printk(KERN_ERR "%s: irq %d for unknown device.\n", __FUNCTION__, irq);
-	goto out;
+
+	return IRQ_HANDLED;
 }
 
 static int wl3501_reset_board(struct wl3501_card *this)