clk: sunxi-ng: h6: Preset hdmi-cec clock parent

H6 manual and BSP clock driver both states that hdmi-cec clock has two
possible parents, osc32k and pll-periph0-2x with 36621 predivider.
Because pll-periph0-2x is always 1.2 GHz, both parents give same
hdmi-cec rate - 32768 Hz, which is exactly the rate needed for HDMI CEC
controller to operate correctly.

However, for some reason, HDMI CEC controller doesn't work if default
parent (osc32k) is used. BSP HDMI driver also always use pll-periph0-2x
as hdmi-cec clock parent.

In order to solve the issue, preset hdmi-cec clock parent to
pll-periph0-2x.

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>