iio: amplifiers: ada4250: move offset_uv in struct

Move offset_uv in struct ada4250_state. This keeps things logically
grouped and reduces holes in the struct.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20250611-iio-amplifiers-ada4250-simplify-data-buffer-in-init-v3-4-bf85ddea79f2@baylibre.com


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