drm/exynos/ipp: remove only related commands on file close

On file close driver should remove only command nodes created
via this file.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Reviewed-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>