drm/exynos/mixer: fix synchronization check in interlaced mode

In case of interlace mode video processor registers and mixer config
register must be check to ensure internal state is in sync with shadow
registers.
This patch fixes page-faults in interlaced mode.

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