virtio-serial: Don't clear ->have_data() pointer after unplug

After a port unplug operation, the port->info->have_data() pointer was
set to NULL.  The problem is, the ->info struct is shared by all ports,
effectively disabling writes to other ports.

Reported-by: juzhang <juzhang@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>

hw/virtio-console.c

@@ -82,7 +82,6 @@ static int virtconsole_exitfn(VirtIOSerialPort *port)
     VirtConsole *vcon = DO_UPCAST(VirtConsole, port, port);
 
     if (vcon->chr) {
-        port->info->have_data = NULL;
         qemu_chr_close(vcon->chr);
     }