dt-bindings: display/msm: hdmi: Fix constraints on additional 'port' properties

The MSM HDMI port nodes are missing any restrictions on additional
properties. The $ref should be to "/properties/port" rather than
"/$defs/port-base" as there are not additional properties in the nodes
to define.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/652299/
Link: https://lore.kernel.org/r/20250507215912.2748964-1-robh@kernel.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>