drm/tegra: Use proper arguments for DRM_TEGRA_CLOSE_CHANNEL IOCTL

A separate data structure exists for the DRM_TEGRA_CLOSE_CHANNEL IOCTL,
but it is currently unused. The IOCTL was using the data structure for
the DRM_TEGRA_OPEN_CHANNEL IOCTL.

Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
Tested-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>