greybus: camera: Stream config change unipro speed

Unipro network speed was increased at camera initialization time and
never slowed down.
This unnecessary drains power during the entire time camera module is
plugged in.
Increasing/decreasing unipro link speed before issuing stream
configuration request to camera module prevents this from happening.

Signed-off-by: Jacopo Mondi <jacopo.mondi@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>