dt-bindings/display: abt,y030xx067a: Fix binding

dt-bindings/display: abt,y030xx067a: Fix binding

The binding should use "unevaluatedProperties" instead of
"additionalProperties", since it is a SPI device and may have
SPI-related Device Tree properties, for instance the "spi-max-frequency"
property that is present in the example.

Fixes: e366a644c69d ("dt-bindings: display: Add ABT Y030XX067A panel bindings")
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://lore.kernel.org/r/20201217005945.335111-1-paul%40crapouillou.net
Signed-off-by: Rob Herring <robh@kernel.org>