[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 99c9e0a1
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>