Transitioned power state logged at the end of setting ACPI power.

However, D3cold won't be in the message because state can only be
D3hot at most.

Use target_state to corretly report when power state is D3cold.

Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>