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/pcmcia/axnet_cs.c b/drivers/net/pcmcia/axnet_cs.c
index e5f3669..5ddd574 100644
--- a/drivers/net/pcmcia/axnet_cs.c
+++ b/drivers/net/pcmcia/axnet_cs.c
@@ -1201,14 +1201,8 @@
 	struct ei_device *ei_local;
     	int handled = 0;
 
-	if (dev == NULL) 
-	{
-		printk ("net_interrupt(): irq %d for unknown device.\n", irq);
-		return IRQ_NONE;
-	}
-    
 	e8390_base = dev->base_addr;
-	ei_local = (struct ei_device *) netdev_priv(dev);
+	ei_local = netdev_priv(dev);
 
 	/*
 	 *	Protect the irq test too.