dt-bindings: media: adv7180: Add missing video-interfaces.yaml reference

The adv7180 binding is using 'bus-width' property, but doesn't document it.
Add a reference to the video-interfaces.yaml schema to properly document it.

Fixes: 066a94e2 ("media: dt-bindings: media: Use graph and video-interfaces schemas")
Cc: Lars-Peter Clausen <lars@metafoo.de>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: linux-media@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210623164256.2569839-1-robh@kernel.org