dt-bindings:iio:afe:current-sense-shunt: txt to yaml conversion.

Very simple binding. As such straight forward conversion.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Peter Rosin <peda@axentia.se>
Link: https://lore.kernel.org/r/20201031181242.742301-7-jic23@kernel.org