test: Fix resource leak in qemumonitorjsontest

Introduced by commmit id 37bd4571c. Need to goto cleanup and
not return directly.

Found by Coverity

Signed-off-by: John Ferlan <jferlan@redhat.com>
Reviewed-by: Katerina Koukiou <kkoukiou@redhat.com>

tests/qemumonitorjsontest.c

@@ -2693,7 +2693,7 @@ testQemuMonitorCPUInfo(const void *opaque)
 
     vm = qemuMonitorTestGetDomainObj(test);
     if (!vm)
-        return -1;
+        goto cleanup;
 
     rc = qemuMonitorGetCPUInfo(qemuMonitorTestGetMonitor(test),
                                &vcpus, data->maxvcpus, true, data->fast);