lis3lv02d: DT: use s32 to support negative values

st,axis-{x,y,z} can be negative to imply inverted
axis.

Apart from that the minimal and maximal threshold
may be negative.

Signed-off-by: Sebastian Reichel <sre@kernel.org>
Reviewed-by: Éric Piel <eric.piel@tremplin-utc.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>