iio: amplifiers: ada4250: use devm_regulator_get_enable_read_voltage()

iio: amplifiers: ada4250: use devm_regulator_get_enable_read_voltage()

Use devm_regulator_get_enable_read_voltage() to simplify the code.

Replace 1000000 with MICRO while we are touching this for better
readability.

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-v3-3-bf85ddea79f2@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>