iio: mlx96014: Replace offset sign

Changed the offset to negative as usual equation is: (raw +
offset)*scale and in this
case offset should be negative (as we deduct 273.15 Kelvin to get temperature
in Celsius).
Signed-off-by: Crt Mori <cmo@melexis.com>
Acked-by: Peter Meerwald <pmeerw@pmeerw.net>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/temperature/mlx90614.c

@@ -204,7 +204,7 @@ static int mlx90614_read_raw(struct iio_dev *indio_dev,
 		*val = ret;
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_OFFSET:
-		*val = 13657;
+		*val = -13657;
 		*val2 = 500000;
 		return IIO_VAL_INT_PLUS_MICRO;
 	case IIO_CHAN_INFO_SCALE: