clk: thead: Correct parent for DPU pixel clocks

clk: thead: Correct parent for DPU pixel clocks

The dpu0_pixelclk and dpu1_pixelclk gates were incorrectly parented to
the video_pll_clk.

According to the TH1520 TRM, the "dpu0_pixelclk" should be sourced from
"DPU0 PLL DIV CLK". In this driver, "DPU0 PLL DIV CLK" corresponds to
the `dpu0_clk` clock, which is a divider whose parent is the
`dpu0_pll_clk`.

This patch corrects the clock hierarchy by reparenting `dpu0_pixelclk`
to `dpu0_clk`. By symmetry, `dpu1_pixelclk` is also reparented to its
correct source, `dpu1_clk`.

Fixes: 50d4b157fa96 ("clk: thead: Add clock support for VO subsystem in T-HEAD TH1520 SoC")
Reported-by: Icenowy Zheng <uwu@icenowy.me>
Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
[Icenowy: add Drew's R-b and rebased atop ccu_gate refactor]
Reviewed-by: Drew Fustini <fustini@kernel.org>
Signed-off-by: Icenowy Zheng <uwu@icenowy.me>
Signed-off-by: Drew Fustini <fustini@kernel.org>