[SCSI] sym53c8xx: fix bogus free_irq() on error path

If sym_attach() gets an error at or before request_irq(), then
sym_free_resources() will call free_irq() for an unregistered
interrupt handler.

Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>