iio: imu: st_lsm6dsx: fix array size for st_lsm6dsx_settings fields

iio: imu: st_lsm6dsx: fix array size for st_lsm6dsx_settings fields

The `decimator` and `batch` fields of struct st_lsm6dsx_settings
are arrays indexed by sensor type, not by sensor hardware
identifier; moreover, the `batch` field is only used for the
accelerometer and gyroscope.
Change the array size for `decimator` from ST_LSM6DSX_MAX_ID to
ST_LSM6DSX_ID_MAX, and change the array size for `batch` from
ST_LSM6DSX_MAX_ID to 2; move the enum st_lsm6dsx_sensor_id
definition so that the ST_LSM6DSX_ID_MAX value is usable within
the struct st_lsm6dsx_settings definition.

Fixes: 801a6e0af0c6c ("iio: imu: st_lsm6dsx: add support to LSM6DSO")
Signed-off-by: Francesco Lavra <flavra@baylibre.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>