drm/rockchip: Don't change hdmi reference clock rate

The code that changes hdmi->ref_clk was accidentally copied from
downstream code that sets a different clock. We don't actually
want to set any clock here at all.

Setting this clock incorrectly leads to incorrect timings for
DDC, CEC, and HDCP signal generation.

No Fixes listed, as the theoretical timing error in DDC appears to
still be within tolerances and harmless - and HDCP and CEC are not
yet supported.

Signed-off-by: Derek Foreman <derek.foreman@collabora.com>
Reviewed-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20241217201708.3320673-1-derek.foreman@collabora.com