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/sb1000.c b/drivers/net/sb1000.c
index dc30dee..b9fa4fb 100644
--- a/drivers/net/sb1000.c
+++ b/drivers/net/sb1000.c
@@ -1084,19 +1084,13 @@
 	char *name;
 	unsigned char st;
 	int ioaddr[2];
-	struct net_device *dev = (struct net_device *) dev_id;
+	struct net_device *dev = dev_id;
 	struct sb1000_private *lp = netdev_priv(dev);
 
 	const unsigned char Command0[6] = {0x80, 0x2c, 0x00, 0x00, 0x00, 0x00};
 	const unsigned char Command1[6] = {0x80, 0x2e, 0x00, 0x00, 0x00, 0x00};
 	const int MaxRxErrorCount = 6;
 
-	if (dev == NULL) {
-		printk(KERN_ERR "sb1000_interrupt(): irq %d for unknown device.\n",
-			irq);
-		return IRQ_NONE;
-	}
-
 	ioaddr[0] = dev->base_addr;
 	/* mem_start holds the second I/O address */
 	ioaddr[1] = dev->mem_start;