iio: imu: st_lsm6dsx: use i2c/spi device name for iio_dev name

Use the correct chip name (e.g. lsm6dsm) as suffix for iio_dev name
instead of a generic one (lsm6dsx)

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@st.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>