After migration the chain4 alias mapping added by 80763888 (in 2011)
might be missing, since there's no call to vga_update_memory_access
in the post_load after the registers are updated.  Add it back.
Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: NJuan Quintela <quintela@redhat.com>
Message-id: 20170804113329.13609-1-dgilbert@redhat.com
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>