markers: probe example, fix teardown

Need a marker_synchronize_unregister() before the end of exit() to make sure
every probe callers have exited the non preemptible section and thus are not
executing the probe code anymore.
Signed-off-by: NMathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

samples/markers/probe-example.c

@@ -81,6 +81,7 @@ static void __exit probe_fini(void)
 			probe_array[i].probe_func, &probe_array[i]);
 	printk(KERN_INFO "Number of event b : %u\n",
 			atomic_read(&eventb_count));
+	marker_synchronize_unregister();
 }
 
 module_init(probe_init);