iio: light: zopt2201: make zopt2201_scale const

Add const qualifier to struct zopt2201_scale zopt2201_scale_*[]. This
is read-only data so it can be made const.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20250628-iio-const-data-22-v1-1-fc9ebdc5f5c3@baylibre.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>