dt-bindings:iio:potentiometer:adi,ad5272 yaml conversion

Simple direct conversion from txt to yaml as part of a general aim of
converting all IIO bindings to this machine readable format.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Phil Reid <preid@electromag.com.au>
Cc: Phil Reid <preid@electromag.com.au>
Link: https://lore.kernel.org/r/20201031184854.745828-3-jic23@kernel.org