drm/exynos: propagate plane initialization errors

In case of error during plane initialization load callback
incorrectly return success, this patch fixes it.

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

diff --cc drivers/gpu/drm/exynos/exynos_drm_drv.c
Simple merge