iio: imu: st_lsm6dsx: use dev_to_iio_dev() to get iio_dev struct

dev_get_drvdata() on iio_dev->dev no longer returns the iio_dev.
Use dev_to_iio_dev() to get iio_dev struct.

Fixes: 8b7651f2 ("iio: iio_device_alloc(): Remove unnecessary self drvdata")
Signed-off-by: Haibo Chen <haibo.chen@nxp.com>
Link: https://lore.kernel.org/r/1645702191-9400-1-git-send-email-haibo.chen@nxp.com


Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>