ui: fix regression in printing VNC host/port on startup

If VNC is chosen as the compile time default display backend,
QEMU will print the host/port it listens on at startup.
Previously this would look like

  VNC server running on '::1:5900'

but in 04d2529d the ':' was
accidentally replaced with a ';'. This the ':' back.

Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 1465382576-25552-1-git-send-email-berrange@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
(cherry picked from commit 83cf07b0)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>