drivers/sensor: lps2xdf: Fix uninitialized variables

Fix some uninitialized variables calling the proper get()
routine prior the equivalent set() operation.

Fixes: #66791, #66778, #66772.
Coverity-CID: 338119, 338144, 338157.

Signed-off-by: Armando Visconti <armando.visconti@st.com>
3 files changed