monitor: Avoid qerror_report_err() outside QMP command handlers

qerror_report_err() is a transitional interface to help with
converting existing monitor commands to QMP.  It should not be used
elsewhere.  Replace by error_report_err() in HMP command handler
hmp_trace_event().
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>

monitor.c

@@ -889,8 +889,7 @@ static void do_trace_event_set_state(Monitor *mon, const QDict *qdict)
 
     qmp_trace_event_set_state(tp_name, new_state, true, true, &local_err);
     if (local_err) {
-        qerror_report_err(local_err);
-        error_free(local_err);
+        error_report_err(local_err);
     }
 }