ACPI: AC: Rename ACPI device from device to adev

Since transformation from ACPI driver to platform driver there are two
devices on which the driver operates - ACPI device and platform device.
For the sake of reader this calls for the distinction in their naming,
to avoid confusion. Rename device to adev, as corresponding
platform device is called pdev.

Signed-off-by: Michal Wilczynski <michal.wilczynski@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>