drm/rockchip: dw_hdmi: cleanup drm encoder during unbind

This fixes a use-after-free crash during rmmod.

The DRM encoder is embedded inside the larger rockchip_hdmi,
which is allocated with the component. The component memory
gets freed before the main drm device is destroyed. Fix it
by running encoder cleanup before tearing down its container.

Signed-off-by: Toby Chen <tobyc@nvidia.com>
[moved encoder cleanup above clk_disable, similar to bind-error-path]
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230317005126.496-1-tobyc@nvidia.com