util: fix memory leak in virFirewallDInterfaceSetZone()

commit 3bba4825 added the new function virFirewallDInterfaceSetZone()
which calledsends virDBUSCallMethod a DBusMessage** for the reply
message, but doesn't use the reply, and also doesn't free it. Since
this arg is allowed to be NULL, this patch simply sets it to NULL so
we don't have to deal with it.
Signed-off-by: NLaine Stump <laine@laine.org>
Reviewed-by: NAndrea Bolognani <abologna@redhat.com>

src/util/virfirewalld.c

@@ -351,13 +351,12 @@ virFirewallDInterfaceSetZone(const char *iface,
                              const char *zone)
 {
     DBusConnection *sysbus = virDBusGetSystemBus();
-    DBusMessage *reply = NULL;
 
     if (!sysbus)
         return -1;
 
     return virDBusCallMethod(sysbus,
-                             &reply,
+                             NULL,
                              NULL,
                              VIR_FIREWALL_FIREWALLD_SERVICE,
                              "/org/fedoraproject/FirewallD1",