trace: make trace_thread_create() use its function arg

This patch makes trace_thread_create() to use its function arg to
initialize thread.  The other choice is to make this a function to use
void arg, but i prefer this way.
Signed-off-by: NJun Koi <junkoi2004@gmail.com>
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>

trace/simple.c

@@ -363,7 +363,7 @@ static GThread *trace_thread_create(GThreadFunc fn)
     sigfillset(&set);
     pthread_sigmask(SIG_SETMASK, &set, &oldset);
 #endif
-    thread = g_thread_create(writeout_thread, NULL, FALSE, NULL);
+    thread = g_thread_create(fn, NULL, FALSE, NULL);
 #ifndef _WIN32
     pthread_sigmask(SIG_SETMASK, &oldset, NULL);
 #endif