Documentation:devicetree:bindings:iio:dac: Fix val

A correct value for output-range-microvolts is -5 to 5 Volts
not -5 to 5 milivolts

Fixes: e904cc89 ("dt-bindings: iio: dac: AD5766 yaml documentation")
Signed-off-by: Mihail Chindris <mihail.chindris@analog.com>
Reviewed-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Link: https://lore.kernel.org/r/20211007080035.2531-6-mihail.chindris@analog.com


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