arm64: dts: rockchip: drop wrong spdif clock from edp1 on rk3588

As described, the analogix-dp controller on rk3588 only supports 2 clocks
and the edp0 node handles that correctly.

The edp1 node on the other hand seems to have a dangling 3rd clock called
spdif, that probably only exists in the vendor-tree.

As that is not handled at all, remove it for now so that we adhere to the
binding.

Fixes: a481bb0b ("arm64: dts: rockchip: Add eDP1 dt node for rk3588")
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20250509152329.2004073-1-heiko@sntech.de