debugfs: Change debuhgfs directory of trace-events-sample.h

Default directory of debug filesystem for ftrace is /sys/kernel/debug/.
Signed-off-by: GeunSik Lim <geunsik.lim@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

samples/trace_events/trace-events-sample.h

 /*
  * If TRACE_SYSTEM is defined, that will be the directory created
- * in the ftrace directory under /debugfs/tracing/events/<system>
+ * in the ftrace directory under /sys/kernel/debug/tracing/events/<system>
  *
  * The define_trace.h below will also look for a file name of
  * TRACE_SYSTEM.h where TRACE_SYSTEM is what is defined here.