dt-bindings: iio: dac: fix ad354xr output range

Fix output range, as per datasheet must be -2.5 to 7.5.

Signed-off-by: Angelo Dureghello <adureghello@baylibre.com>
Fixes: b0a96c5f

 ("dt-bindings: iio: dac: Add adi,ad3552r.yaml")
Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20240503185528.2043127-1-adureghello@baylibre.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>