ARM: dts: sun8i: drop A64 HDMI PHY fallback compatible from R40 DT

The R40 HDMI PHY seems to be different to the A64 one, the A64 one
has no input mux, but the R40 one has.

Drop the A64 fallback compatible from the HDMI PHY node in R40 DT.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
[wens@csie.org: Fix subject prefix order]
Signed-off-by: Chen-Yu Tsai <wens@csie.org>