qxl: Add missing '\n' to qxl_io_log() call

The message has to be terminated by a newline as it's not going to get
added automatically.

Signed-off-by: Christophe Fergeau <cfergeau@redhat.com>
Acked-by: Frediano Ziglio <fziglio@redhat.com>
Message-id: 20161108091209.25568-4-cfergeau@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>