libxl: fix build failure due to change in virDomainGraphicsDef

This failure was introduced by commit dacee3d, which removed
listenAddr from the unions in virDomainGraphicsDef in favor of putting
it in the address attribute of virDomainGraphicsListenDef.

src/libxl/libxl_conf.c

@@ -651,6 +651,7 @@ libxlMakeVfb(libxlDriverPrivatePtr driver, virDomainDefPtr def,
              virDomainGraphicsDefPtr l_vfb, libxl_device_vfb *x_vfb)
 {
     int port;
+    const char *listenAddr;
 
     switch (l_vfb->type) {
         case VIR_DOMAIN_GRAPHICS_TYPE_SDL:
@@ -682,11 +683,11 @@ libxlMakeVfb(libxlDriverPrivatePtr driver, virDomainDefPtr def,
             }
             x_vfb->vncdisplay = l_vfb->data.vnc.port - LIBXL_VNC_PORT_MIN;
 
-            if (l_vfb->data.vnc.listenAddr) {
+            listenAddr = virDomainGraphicsListenGetAddress(l_vfb, 0);
+            if (listenAddr) {
                 /* libxl_device_vfb_init() does strdup("127.0.0.1") */
                 free(x_vfb->vnclisten);
-                if ((x_vfb->vnclisten =
-                    strdup(l_vfb->data.vnc.listenAddr)) == NULL) {
+                if ((x_vfb->vnclisten = strdup(listenAddr)) == NULL) {
                     virReportOOMError();
                     return -1;
                 }