PM / devfreq: Unlock mutex and free devfreq struct in error path

The devfreq->lock is held for time of setup. Release the lock in the
error path, before jumping to the end of the function.

Change the goto destination which frees the allocated memory.

Cc: v5.9+ <stable@vger.kernel.org> # v5.9+
Fixes: 4dc3bab8 ("PM / devfreq: Add support delayed timer for polling mode")
Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>