bdinfo: dm: Update fb_base when using driver model

Update this value with the address of a video device so that it shows with
the 'bd' command.

It would be better to obtain the address from the uclass by looking in
struct video_uc_platdata for each device. We can move over to that once
DM_VIDEO migration is complete.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>