Driver core: keep PHYSDEV for old struct class_device

Class-devices created by "struct class_device" are going to be replaced
by "struct device". Keep the deprecated PHYSDEV* variables for the already
"deprecated" struct class_device" devices.

Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>