Fix some cut-and-paste errors in the OS deprecation warning
pointed out by Thomas Huth.

Reported-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1490119729-26206-1-git-send-email-peter.maydell@linaro.org