iio: imu: st_lsm6dsx: use st_lsm6dsx_read_locked in st_lsm6dsx_report_motion_event

Rely on st_lsm6dsx_read_locked in st_lsm6dsx_report_motion_event since
it can run concurrently with sensor hub configuration. Move event
related code in st_lsm6dsx_report_motion_event

Fixes: 1aabad1f ("iio: imu: st_lsm6dsx: add motion report function and call from interrupt")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Tested-by: Sean Nyekjaer <sean@geanix.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>