drivers: iio: dac: ad5766: Fix dt property name

In the documentation the name for the property is
output-range-microvolts which is a standard name, therefore this name
must be used.

Fixes: fd9373e4 ("iio: dac: ad5766: add driver support for AD5766")
Signed-off-by: Mihail Chindris <mihail.chindris@analog.com>
Reviewed-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Link: https://lore.kernel.org/r/20211007080035.2531-5-mihail.chindris@analog.com


Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>