dt-bindings: iio: adc: ad7476: Drop redundant prop: true

dt-bindings: iio: adc: ad7476: Drop redundant prop: true

The ad7476 supports a few variants with different power-supplies and
control GPIOs. The binding first unconditionally introduces all the
properties, and later sets them 'true' or 'false' based on the
combatible.

The 'true' seems to be implied by the initial property introduction so
the 'true' -branches in later conditional handling (based on the
compatible) can be omitted.

Drop the redundant true -branches.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://patch.msgid.link/bee66444bf628ba9a34a02738a1842e2abc14290.1754901948.git.mazziesaccount@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>