iio: amplifiers: ad8366: Fix ADRF5720/30/31 gain calculation

This fixes and inverted gain read.

Fixes: f4a69c8 ("iio: amplifiers: ad8366: Update device support")

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>

Author: mhennerich

drivers/iio/amplifiers/ad8366.c

@@ -181,10 +181,10 @@ static int ad8366_read_raw(struct iio_dev *indio_dev,
 			break;
 		case ID_ADRF5720:
 		case ID_ADRF5730:
-			gain = -31500 + code * 500;
+			gain = -1 * code * 500;
 			break;
 		case ID_ADRF5731:
-			gain = -30000 + code * 500;
+			gain = -1 * code * 500;
 			break;
 		case ID_HMC792:
 			gain = -1 * code * 500;