Correct the comment about userspace function which triggers the latency tracer

Signed-off-by: Luotao Fu <lfu@pengutronix.de>

Index: linux-2.6.18-rt.sec/kernel/latency_trace.c
===================================================================
--- kernel/latency_trace.c
+++ kernel/latency_trace.c
@@ -263,7 +263,7 @@ int trace_all_cpus = 0;
 int print_functions = 0;
 
 /*
- * user-triggered via gettimeofday(0,1)/gettimeofday(0,0)
+ * user-triggered via prctl(0,1)/prctl(0,0)
  */
 int trace_user_triggered = 0;
 int trace_user_trigger_irq = -1;