base: Fix VNC server initialization

In a previous commit, the initialization of dataFd to -1 is removed.
Add it back so VNC server can properly accept connection.

Fixes: 67fb75d659 ("base,cpu,dev,sim: Pull common logic into ListenSocket::listen().")
Change-Id: I4246d1fddc766cb190a04d4f984fc1ce73af3fb0
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/69757
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>

src/base/vnc/vncserver.cc

@@ -117,7 +117,7 @@ VncServer::DataEvent::process(int revent)
  */
 VncServer::VncServer(const Params &p)
     : VncInput(p), listenEvent(NULL), dataEvent(NULL), number(p.number),
-      listener(p.port.build(p.name)),
+      dataFd(-1), listener(p.port.build(p.name)),
       sendUpdate(false), supportsRawEnc(false), supportsResizeEnc(false)
 {
     if (p.port)