PM / devfreq: fix double kfree

When device_register() fails, kfree(devfreq) is called already in
devfreq_dev_release(), hence there is no need to call kfree(devfreq)
in err_dev again.

Signed-off-by: Geliang Tang <geliangtang@163.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>