Various drivers' irq handlers: kill dead code, needless casts

- Eliminate casts to/from void*

- Eliminate checks for conditions that never occur.  These typically
  fall into two classes:

	1) Checking for 'dev_id == NULL', then it is never called with
	NULL as an argument.

	2) Checking for invalid irq number, when the only caller (the
	system) guarantees the irq handler is called with the proper
	'irq' number argument.

Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/sn/ioc3.c

@@ -401,7 +401,7 @@ static inline uint32_t get_pending_intrs(struct ioc3_driver_data *idd)
 static irqreturn_t ioc3_intr_io(int irq, void *arg)
 {
 	unsigned long flags;
-	struct ioc3_driver_data *idd = (struct ioc3_driver_data *)arg;
+	struct ioc3_driver_data *idd = arg;
 	int handled = 1, id;
 	unsigned int pending;