drm/rockchip: analogix_dp: add missing clk_disable_unprepare() on error

Add the missing clk_disable_unprepare() before return in the
error handling case.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Sean Paul <seanpaul@chromium.org>