iio:magnetometer: bugfix magnetometers gain values

This patch fix gains values. The first driver was designed using
engineering samples, in mass production the values are changed.

Signed-off-by: Denis Ciocca <denis.ciocca@st.com>
Cc: Stable@vger.kernel.org
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
1 file changed