iio: st_lsm6dsx: Fixed calibrated timestamp calculation

iio: st_lsm6dsx: Fixed calibrated timestamp calculation

The calibrated timestamp is calculated from the nominal value using the
formula:
  ts_gain[ns] ≈ ts_sensitivity - (ts_trim_coeff * val) / 1000.

The values of ts_sensitivity and ts_trim_coeff are not the same for all
devices, so it is necessary to differentiate them based on the part name.
For the correct values please consult the relevant AN.

Fixes: cb3b6b8e1bc0 ("iio: imu: st_lsm6dsx: add odr calibration feature")
Signed-off-by: Mario Tesi <mario.tesi@st.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>