Add missing reg property and update example to add dsi top node.

Fixes: ef85db91 ("dt-bindings: display: panel: document the Visionox VTDR6130 AMOLED DSI Panel")
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230207-topic-sm8550-upstream-vtdr6130-bindings-fix-v1-1-0ba2323420c5@linaro.org