drm/exynos/ipp: correct address type

exynos_drm_gem_get_dma_addr returns dma_addr_t, type casting to void* and
back is not necessary.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>