libata: fix unbalanced spin_lock_irqsave/spin_unlock_irq() in ata_scsi_park_show()

ata_scsi_park_show() was pairing spin_lock_irqsave() with
spin_unlock_irq().  As the function is always called with irq enabled,
it didn't actually break anything.  Use spin_lock_irq() instead.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Elias Oltmanns <eo@nebensachen.de>