rockchip: add a dummy byte for the sdram-channel property

Add an extra byte so that this data is not byteswapped.

Signed-off-by: Ziyuan Xu <jk.kernel@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Ziyuan Xu <xzy.xu@rock-chips.com>