Rename the "allocate and return" qbus creation function to
qbus_new(), to bring it into line with our _init vs _new convention.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Corey Minyard <cminyard@mvista.com>
Message-id: 20210923121153.23754-6-peter.maydell@linaro.org