[SCSI] aha152x, eata, u14-34f: minor irq handler cleanups

- remove pointless casts from void*

- remove needless references to 'irq' function argument, when that
  information is already stored somewhere in a driver-private struct.

- where the 'irq' function argument is known never to be used, rename
  it to 'dummy' to make this more obvious

- remove always-false tests for dev_id==NULL

- remove always-true tests for 'irq == host_struct->irq'

- replace per-irq lookup functions and tables with a direct reference
  to data object obtained via 'dev_id' function argument, passed from
  request_irq()

This change's main purpose is to prepare for the patchset in
jgarzik/misc-2.6.git#irq-remove, that explores removal of the
never-used 'irq' argument in each interrupt handler.

Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

drivers/scsi/aha152x.c

@@ -1432,15 +1432,10 @@ static void run(struct work_struct *work)
  */
 static irqreturn_t intr(int irqno, void *dev_id)
 {
-	struct Scsi_Host *shpnt = (struct Scsi_Host *)dev_id;
+	struct Scsi_Host *shpnt = dev_id;
 	unsigned long flags;
 	unsigned char rev, dmacntrl0;
 
-	if (!shpnt) {
-		printk(KERN_ERR "aha152x: catched interrupt %d for unknown controller.\n", irqno);
-		return IRQ_NONE;
-	}
-
 	/*
 	 * Read a couple of registers that are known to not be all 1's. If
 	 * we read all 1's (-1), that means that either: