testCompareMemLock: Use correct free function for domain def

virDomainDef is not an instance of virObject thus
virObjectUnref() is not the correct function to be called.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

tests/qemumemlocktest.c

@@ -50,7 +50,7 @@ testCompareMemLock(const void *data)
     ret = virTestCompareToULL(info->memlock, qemuDomainGetMemLockLimitBytes(def));
 
  cleanup:
-    virObjectUnref(def);
+    virDomainDefFree(def);
     VIR_FREE(xml);
 
     return ret;