genirq: Document IRQCHIP_ONESHOT_SAFE flag

Add missing documentation of the flag.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/include/linux/irq.h b/include/linux/irq.h
index e675971..67ace7a 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -355,6 +355,7 @@
  * IRQCHIP_ONOFFLINE_ENABLED:	Only call irq_on/off_line callbacks
  *				when irq enabled
  * IRQCHIP_SKIP_SET_WAKE:	Skip chip.irq_set_wake(), for this irq chip
+ * IRQCHIP_ONESHOT_SAFE:	One shot does not require mask/unmask
  */
 enum {
 	IRQCHIP_SET_TYPE_MASKED		= (1 <<  0),