iio: imu: st_lsm6dsx: add addr/max_word_len to st_lsm6dsx_read_block()

Add reg addr and max_word_len parameters to st_lsm6dsx_read_block
since LSM6DSO will use a different register address to read samples
from the FIFO and a different sample len

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>