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>
diff --git a/drivers/atm/lanai.c b/drivers/atm/lanai.c
index 8895f02..2678255 100644
--- a/drivers/atm/lanai.c
+++ b/drivers/atm/lanai.c
@@ -1892,11 +1892,9 @@
 
 static irqreturn_t lanai_int(int irq, void *devid)
 {
-	struct lanai_dev *lanai = (struct lanai_dev *) devid;
+	struct lanai_dev *lanai = devid;
 	u32 reason;
 
-	(void) irq;	/* unused variables */
-
 #ifdef USE_POWERDOWN
 	/*
 	 * If we're powered down we shouldn't be generating any interrupts -