IIO: st_accel_i2c.c: Simplify access to driver data

Use device_get_match_data API to simplify access to driver data.
Let acpi_device_id table entries point to the same driver data as
of_device_id table entries and uniquify access to driver data by using
device_get_match_data API. Remove unused i2c_device_id .driver_data
fields.

Signed-off-by: Nikolaus Voss <nikolaus.voss@loewensteinmedical.de>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>