ACPI / DPTF: Use dev_get_drvdata()

Skip conversion to platform_device and use dev_get_drvdata() directly.

Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
[ rjw: Changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>