PM / devfreq: Fix memory leak when fail to register device

PM / devfreq: Fix memory leak when fail to register device

When the devfreq_add_device fails to register deivce, the memory
leak of devfreq instance happen. So, this patch fix the memory
leak issue. Before freeing the devfreq instance checks whether
devfreq instance is NULL or not because the device_unregister()
frees the devfreq instance when jumping to the 'err_init'.
It is to prevent the duplicate the kfee(devfreq).

Cc: stable@vger.kernel.org
Fixes: ac4b281176a5 ("PM / devfreq: fix duplicated kfree on devfreq pointer")
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>