drm/rockchip: rk3066_hdmi: Remove useless mode_fixup

The mode_fixup implementation doesn't do anything, so we can simply
remove it.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/5649ac03-db92-42a9-d86a-76dfa1af7c64@gmail.com