ACPI / PM: Fix device power state value after transitions to D3cold

When a transition to the D3cold power state is requested,
acpi_device_set_power() first carries out a transition to D3hot and
then turns off the device's power resources.  However, it fails to
update the device's power.state field appropriately and D3hot is
stored in it as a result.

Fix this, but make sure that the device's power state will be
D3hot if its power resources cannot be turned off in the final
step.

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