drm/bridge: anx7625: Fix release wrong workqueue

If "hdcp_workqueue" exist, must release "hdcp_workqueue",
not "workqueue".

Fixes: cd1637c7 ("drm/bridge: anx7625: add HDCP support")
Signed-off-by: Xin Ji <xji@analogixsemi.com>
Reviewed-by: Hsin-Yi Wang <hsinyi@chromium.org>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220217024418.3780171-1-xji@analogixsemi.com