clocksource/drivers/orion: Add missing clk_disable_unprepare() on error path

After calling clk_prepare_enable(), clk_disable_unprepare() need
be called on error path.

Fixes: fbe4b356 ("clocksource/drivers/orion: Convert init function...")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20201111064706.3397156-1-yangyingliang@huawei.com