dt-bindings: phy: drop #clock-cells from rockchip,px30-dsi-dphy

Further review of the dsi components for the px30 revealed that the
phy shouldn't expose the pll as clock but instead handle settings
via phy parameters.

As the phy binding is new and not used anywhere yet, just drop them
so they don't get used.

Fixes: 3817c796 ("dt-bindings: phy: add yaml binding for rockchip,px30-dsi-dphy")
Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>