clockevents: Add missing parameter documentation

Add the missing documentation for the @cpu parameter of
tick_cleanup_dead_cpu().

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210608024305.2750999-1-libaokun1@huawei.com

kernel/time/clockevents.c

@@ -629,6 +629,7 @@ void tick_offline_cpu(unsigned int cpu)
 
 /**
  * tick_cleanup_dead_cpu - Cleanup the tick and clockevents of a dead cpu
+ * @cpu:	The dead CPU
  */
 void tick_cleanup_dead_cpu(int cpu)
 {