drm/hisilicon: Make kirin_drm_unbind sufficient

Remove deprecated drm_put_dev.
Clean up everything needed in unbind.
Thanks to Daniel Vetter, this issue is reported by him.

Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reported-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Xinliang Liu <xinliang.liu@linaro.org>