genirq: Fix typo in documentation of enumeration field name

It should say IRQ_NESTED_THREAD instead of IRQ_NESTED_TRHEAD.
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: Jiang Liu <jiang.liu@linux.intel.com>
Link: http://lkml.kernel.org/r/1443704093-36837-1-git-send-email-mika.westerberg@linux.intel.comSigned-off-by: Thomas Gleixner <tglx@linutronix.de>

include/linux/irq.h

@@ -67,7 +67,7 @@ enum irqchip_irq_state;
  *				  request/setup_irq()
  * IRQ_NO_BALANCING		- Interrupt cannot be balanced (affinity set)
  * IRQ_MOVE_PCNTXT		- Interrupt can be migrated from process context
- * IRQ_NESTED_TRHEAD		- Interrupt nests into another thread
+ * IRQ_NESTED_THREAD		- Interrupt nests into another thread
  * IRQ_PER_CPU_DEVID		- Dev_id is a per-cpu variable
  * IRQ_IS_POLLED		- Always polled by another interrupt. Exclude
  *				  it from the spurious interrupt detection