ARM: dts: sun6i: Set PLL6 as parent to AHB1 clock in AHB1 clock node

On sun6i we already have PLL6 as AHB1 clock's parent. However this was
previously set in the dma controller node, which takes effect when the
dma controller is probed.

We want this to take effect as soon as possible, so hrtimer rate
calculation is correct, and to be sure the AHB1 clock rate remains as
stable as possible.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>