greybus: raw: fix memory leak on disconnect

Make sure the class device is freed as well as deregistered on
disconnect.

Also deregister the class device before character device as the former
depends on the latter.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>