drm/vc4: vec: Remove redundant atomic_mode_set

Let's remove the superfluous tv_mode field, which was redundant with the
mode field in struct drm_tv_connector_state.

Signed-off-by: Mateusz Kwiatkowski <kfyatek+publicgit@gmail.com>
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220728-rpi-analog-tv-properties-v2-27-459522d653a7@cerno.tech