drm/rockchip: allocate correct crtc state structure on reset

Because we are using a custom crtc_state structure, we must override the
reset helper to allocate the correct amount of memory.

Cc: stable@vger.kernel.org
Fixes: 4e257d9e ("drm/rockchip: get rid of rockchip_drm_crtc_mode_config")
Signed-off-by: John Keeping <john@metanate.com>
Signed-off-by: Mark Yao <mark.yao@rock-chips.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>