tests: qemuMonitorReportError: use tmp variable properly

There is no obvious benefit in putting the escaped message
back into msg while tmp holds the original message.

Remove the assignment and use 'tmp' directly'.
Signed-off-by: NJán Tomko <jtomko@redhat.com>

tests/qemumonitortestutils.c

@@ -213,16 +213,14 @@ qemuMonitorReportError(qemuMonitorTestPtr test, const char *errmsg, ...)
         goto cleanup;
 
     if (test->agent || test->json) {
-        char *tmp = msg;
-        msg = qemuMonitorEscapeArg(tmp);
-        VIR_FREE(tmp);
-        if (!msg)
+        VIR_AUTOFREE(char *) tmp = NULL;
+        if (!(tmp = qemuMonitorEscapeArg(msg)))
             goto cleanup;
 
         if (virAsprintf(&jsonmsg, "{ \"error\": "
                                   " { \"desc\": \"%s\", "
                                   "   \"class\": \"UnexpectedCommand\" } }",
-                                  msg) < 0)
+                                  tmp) < 0)
             goto cleanup;
     } else {
         if (virAsprintf(&jsonmsg, "error: '%s'", msg) < 0)