drm/exynos/hdmi: remove redundant mode field

Display mode is preserved in CRTC state, there is no need to keep local
copy of it. Moreover since HDMI should configure registers according to
requested mode, use it instead of adjusted_mode, which should contain
mode produced by CRTC - functionally it does not change anything, but
subsequent patches will make the difference.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Reviewed-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Signed-off-by: Inki Dae <inki.dae@samsung.com>