iio: st_sensors: fix scale configuration for h3lis331dl

fix scale configuration/parsing for h3lis331dl accel driver
when sensitivity is higher than 1(m/s^2)/digit

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@st.com>
Fixes: 1e52fefc ("iio: accel: Add support for the h3lis331dl accelerometer")
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>