[SCSI] sym53c8xx: fix free_irq() regression

The following commit changed the pointer passed to request_irq(), but
failed to change the pointer passed to free_irq():

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

    ...

The result is that free_irq() doesn't actually take any action.  This
patch fixes it.

Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Acked-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>