clk: sunxi-ng: sun6i: Rename HDMI DDC clock to avoid name collision

The HDMI DDC clock found in the CCU is the parent of the actual DDC
clock within the HDMI controller. That clock is also named "hdmi-ddc".

Rename the one in the CCU to "ddc". This makes more sense than renaming
the one in the HDMI controller to something else.

Fixes: c6e6c96d ("clk: sunxi-ng: Add A31/A31s clocks")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>