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/scsi/dc395x.c

@@ -1815,7 +1815,7 @@ static void dc395x_handle_interrupt(struct AdapterCtlBlk *acb,
 
 static irqreturn_t dc395x_interrupt(int irq, void *dev_id)
 {
-	struct AdapterCtlBlk *acb = (struct AdapterCtlBlk *)dev_id;
+	struct AdapterCtlBlk *acb = dev_id;
 	u16 scsi_status;
 	u8 dma_status;
 	irqreturn_t handled = IRQ_NONE;