dt-bindings: display: ingenic,jz4780-hdmi: Drop undocumented 'ddc-i2c-bus'

While 'ddc-i2c-bus' is a common property, it should be in a connector
node rather than the HDMI bridge node as the I2C bus goes to a
connector and not the HDMI block. Drop it from the example.

Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220525205626.2482584-1-robh@kernel.org