iio: imu: st_lsm6dsx: move max_fifo_size in st_lsm6dsx_fifo_ops

Move max_fifo_size in st_lsm6dsx_fifo_ops in order to have all
FIFO configuration parameters in st_lsm6dsx_fifo_ops structure.
This patch does not introduce any logic change, just small code
rearrangement.

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://lore.kernel.org/r/3262ad9d9d1497e19ea1bab208c495c2b9a98994.1632664866.git.lorenzo@kernel.org


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>