rockchip: ringneck_px30: update website link

The original link returns a custom 404, so let's point to a link that
works today instead.

Cc: Quentin Schulz <foss+uboot@0leil.net>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>