clk: mediatek: correct the clocks for MT2701 HDMI PHY module

The hdmitx_dig_cts clock signal is not a child of clk26m,
and the actual output of the PLL block is derived from
the tvdpll via a configurable PLL post-divider.

It is used as the PLL reference input to the HDMI PHY module.

Fixes: e9862118

 ("clk: mediatek: Add MT2701 clock support")
Signed-off-by: Chunhui Dai <chunhui.dai@mediatek.com>
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>