dt-bindings: iio: avia-hx711: Fix avdd-supply typo in example

Now that examples are validated against the DT schema, a typo in
avia-hx711 example generates a warning:

Documentation/devicetree/bindings/iio/adc/avia-hx711.example.dt.yaml: weight: 'avdd-supply' is a required property

Fix the typo.

Fixes: 5150ec3f

 ("avia-hx711.yaml: transform DT binding to YAML")
Cc: Andreas Klinger <ak@it-klinger.de>
Cc: Jonathan Cameron <jic23@kernel.org>
Cc: linux-iio@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>