dt-bindings: display: vc4: dpi: Fix panel warning

The example used in the DPI binding before the conversion to YAML had a
simple-panel example that got carried over to the YAML binding.

However, that example doesn't match the simple-panel binding and results in
validation errors. Since it's only marginally helpful, let's remove that
part of the example entirely.

Fixes: 09453600

 ("dt-bindings: display: Convert VC4 bindings to schemas")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200626121131.127192-1-maxime@cerno.tech