dt-bindings: iio: adc: ti,adc128s052 yaml conversion.

Simple binding.  Only addition to txt version is
as a provider of channels to other devices using the consumer
binding.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Angelo Compagnucci <angelo.compagnucci@gmail.com>
Link: https://lore.kernel.org/r/20200809111753.156236-10-jic23@kernel.org