drm/exynos: ipp: use correct enum type

The limit_id_fallback array uses enum drm_ipp_size_id to index its
content. The content itself is of type enum drm_exynos_ipp_limit_type.

Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Inki Dae <inki.dae@samsung.com>