drm/rockchip: dw_hdmi: Call drm_encoder_cleanup() in error path

The drm_encoder_cleanup() was missing both from the error path of
dw_hdmi_rockchip_bind().  This caused a crash when slub_debug was
enabled and we ended up deferring probe of HDMI at boot.

This call isn't needed from unbind() because if dw_hdmi_bind() returns
no error then it takes over the job of freeing the encoder (in
dw_hdmi_unbind).

Signed-off-by: Douglas Anderson <dianders@chromium.org>