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/wavelan_cs.c b/drivers/net/wireless/wavelan_cs.c
index cadfe13..aafb301 100644
--- a/drivers/net/wireless/wavelan_cs.c
+++ b/drivers/net/wireless/wavelan_cs.c
@@ -4119,21 +4119,12 @@
 wavelan_interrupt(int		irq,
 		  void *	dev_id)
 {
-  struct net_device *	dev;
+  struct net_device *	dev = dev_id;
   net_local *	lp;
   kio_addr_t	base;
   int		status0;
   u_int		tx_status;
 
-  if ((dev = dev_id) == NULL)
-    {
-#ifdef DEBUG_INTERRUPT_ERROR
-      printk(KERN_WARNING "wavelan_interrupt(): irq %d for unknown device.\n",
-	     irq);
-#endif
-      return IRQ_NONE;
-    }
-
 #ifdef DEBUG_INTERRUPT_TRACE
   printk(KERN_DEBUG "%s: ->wavelan_interrupt()\n", dev->name);
 #endif