media: dt-bindings: ti,ds90ub960: Allow setting serializer address

The serializer's I2C address on the FPD-Link bus is usually communicated
to the deserializer once the forward-channel is established. But in some
cases it might be necessary to program the serializer (over the
back-channel) before the forward-channel is established.

This can be used e.g. to correct serializer configuration which
otherwise would prevent the FC to be enabled. To be able to communicate
to the serializer before the forward-channel is up, the deserializer
driver neds to know the default i2c address of the serializer.

Allow setting the serializer i2c address using the 'reg' property. This
is optional, and usually not needed.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Jai Luthra <jai.luthra@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>