Fix comment typo "spin_lock_irqrestore".

Fix "spin_lock_irqrestore" to "spin_unlock_irqrestore."
Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>

arch/ia64/kernel/perfmon.c

@@ -147,7 +147,7 @@
  * in UP:
  * 	- we need to protect against PMU overflow interrupts (local_irq_disable)
  *
- * spin_lock_irqsave()/spin_lock_irqrestore():
+ * spin_lock_irqsave()/spin_unlock_irqrestore():
  * 	in SMP: local_irq_disable + spin_lock
  * 	in UP : local_irq_disable
  *