rockchip: video: Remove CSC initialization (HDMI)

Despite the comment in the code, CSC unit is never used. According to
the only public description of DW HDMI controller (i.MX6 manual), CSC
unit is bypassed in MC_FLOWCTRL register and then actually powered
down in MC_CLKDIS register.

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Reviewed-by: Simon Glass <sjg@chromium.org>