[SCSI] sym53c8xx: fix "irq X: nobody cared" regression

The patch described by the following excerpt from ChangeLog-2.6.24-rc1
eventually causes a "irq X: nobody cared" error after a while:

commit 99c9e0a1d6cfe1ba1169a7a81435ee85bc00e4a1
Author: Matthew Wilcox <matthew@wil.cx>
Date:   Fri Oct 5 15:55:12 2007 -0400

    [SCSI] sym53c8xx: Make interrupt handler capable of returning IRQ_NONE

After this happens, the kernel disables the IRQ, causing the SCSI card
to stop working until the next reboot.  The problem is caused by the
interrupt handler returning IRQ_NONE instead of IRQ_HANDLED after
handling an interrupt-on-the-fly (INTF) condition.  The following patch
fixes the problem.

Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Acked-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

drivers/scsi/sym53c8xx_2/sym_hipd.c

@@ -2791,7 +2791,7 @@ irqreturn_t sym_interrupt(struct Scsi_Host *shost)
 	istat = INB(np, nc_istat);
 	if (istat & INTF) {
 		OUTB(np, nc_istat, (istat & SIGP) | INTF | np->istat_sem);
-		istat = INB(np, nc_istat);		/* DUMMY READ */
+		istat |= INB(np, nc_istat);		/* DUMMY READ */
 		if (DEBUG_FLAGS & DEBUG_TINY) printf ("F ");
 		sym_wakeup_done(np);
 	}