cpufreq: mediatek: fix device leak on probe failure

Make sure to drop the reference to the cci device taken by
of_find_device_by_node() on probe failure (e.g. probe deferral).

Fixes: 0daa4732 ("cpufreq: mediatek: Link CCI device to CPU")
Cc: Jia-Wei Chang <jia-wei.chang@mediatek.com>
Cc: Rex-BC Chen <rex-bc.chen@mediatek.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>