perf tools: Fix inverted error verification bug in thread__fork

Commit 1902efe7 for the new comm infra added the wrong check for return
code on thread__set_comm. err == 0 is normal, so don't return at that
point unless err != 0.
Signed-off-by: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/1386736538-23525-1-git-send-email-dsahern@gmail.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/thread.c

@@ -126,7 +126,7 @@ int thread__fork(struct thread *thread, struct thread *parent, u64 timestamp)
 		if (!comm)
 			return -ENOMEM;
 		err = thread__set_comm(thread, comm, timestamp);
-		if (!err)
+		if (err)
 			return err;
 		thread->comm_set = true;
 	}