[SCSI] gdth: Fix obvious typo "spin_lock_irqrestore()"

Fix misspelled "spin_lock_irqrestore" to read "spin_unlock_irqrestore"
instead.

Presumably, GDTH_RTC doesn't get used a lot.

Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
Acked-by: Achim Leubner <achim_leubner@adaptec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>