tracing: Skip printing "OK" if failed to disable event

No acutal case found. But logically, we should skip "OK" in case any
error met.

Link: http://lkml.kernel.org/r/1346051625-25231-1-git-send-email-yuanhan.liu@linux.intel.com



Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>