tracing: Allow dumping traces without tracking trace started cpus

We don't init iter->started when dumping the ftrace buffer, and there's no
real need to do so - so allow skipping that check if the iter doesn't have
an initialized ->started cpumask.

Link: http://lkml.kernel.org/r/1441385156-27279-1-git-send-email-sasha.levin@oracle.com



Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>