drm/exynos: use adjusted_mode of crtc_state instead of mode

Handle changes by removing copy from adjusted_mode to mode as using
adjusted_mode of crtc_state.

Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>