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>

drivers/net/tokenring/tms380tr.c

@@ -751,11 +751,6 @@ irqreturn_t tms380tr_interrupt(int irq, void *dev_id)
 	unsigned short irq_type;
 	int handled = 0;
 
-	if(dev == NULL) {
-		printk(KERN_INFO "%s: irq %d for unknown device.\n", dev->name, irq);
-		return IRQ_NONE;
-	}
-
 	tp = netdev_priv(dev);
 
 	irq_type = SIFREADW(SIFSTS);