PM / devfreq: use put_device() instead of kfree()

Never directly free @dev after calling device_register() or
device_unregister(), even if device_register() returned an error.
Always use put_device() to give up the reference initialized.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>