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/irda/irport.h

@@ -74,7 +74,7 @@ struct irport_cb {
 	/* For piggyback drivers */
 	void *priv;                
 	void (*change_speed)(void *priv, __u32 speed);
-	int (*interrupt)(int irq, void *dev_id);
+	irqreturn_t (*interrupt)(int irq, void *dev_id);
 };
 
 #endif /* IRPORT_H */