PM / devfreq: Send the DEVFREQ_POSTCHANGE notification when target() is failed

This patch sends the DEVFREQ_POSTCHANGE notification when
devfreq->profile->targer() is failed. The PRECHANGE/POSTCHANGE
should be paired.

Fixes: 0fe3a664 (PM / devfreq: Add new DEVFREQ_TRANSITION_NOTIFIER notifier)
Reported-by: Lin Huang <hl@rock-chips.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>