pcc-acpi: fix compile with new stricter ACPI types

This was another merge problem that wasn't a data conflict, but due to
independent changes in two branches that just didn't work together.

The pcc-acpi staging driver used

	acpi_driver_data(device) = hotkey;

to set driver data, but the ACPI merge made that invalid in commit
db89b4f0

 ("ACPI: catch calls of
acpi_driver_data on pointer of wrong type"), and now you're supposed to
just do.

	device->driver_data = hotkey;

instead.

Fix it up.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>