libxl: support VNC passwd

While implementing support for SPICE, I noticed VNC passwd was
never copied to libxl_device_vfb's vnc.passwd field.
Signed-off-by: NJim Fehlig <jfehlig@suse.com>

src/libxl/libxl_conf.c

@@ -1283,6 +1283,8 @@ libxlMakeVfb(virPortAllocatorPtr graphicsports,
                 if (VIR_STRDUP(x_vfb->vnc.listen, listenAddr) < 0)
                     return -1;
             }
+            if (VIR_STRDUP(x_vfb->vnc.passwd, l_vfb->data.vnc.auth.passwd) < 0)
+                return -1;
             if (VIR_STRDUP(x_vfb->keymap, l_vfb->data.vnc.keymap) < 0)
                 return -1;
             break;