au1000_eth: remove useless check

The lifespan of the device covers the request_irq .. free_irq interval.

The cast of a void * pointer is not needed either.
Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/net/au1000_eth.c

@@ -1239,12 +1239,7 @@ static int au1000_rx(struct net_device *dev)
  */
 static irqreturn_t au1000_interrupt(int irq, void *dev_id)
 {
-	struct net_device *dev = (struct net_device *) dev_id;
-
-	if (dev == NULL) {
-		printk(KERN_ERR "%s: isr: null dev ptr\n", dev->name);
-		return IRQ_RETVAL(1);
-	}
+	struct net_device *dev = dev_id;
 
 	/* Handle RX interrupts first to minimize chance of overrun */