simple-bus: enable support for of-platdata

Just do nothing in post_bind if of-platdata enabled,
for there is no dm_scan_fdt_dev().

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Fixed subject line typo:
Signed-off-by: Simon Glass <sjg@chromium.org>