[SCSI] sym53c8xx: Don't disable interrupts in the interrupt handler

Interrupts can't be re-entered, so it's sufficient to call spin_lock, not
spin_lock_irqsave().

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>