tracing: Remove unneeded NULL check

We checked "iter->trace" earlier so there is no need to check here.

Link: http://lkml.kernel.org/r/20141122183012.GB6994@mwanda



Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
[ Pulled from the archeological digging of my INBOX ]
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>