ARM: dts: renesas: Add fck to etheravb-rcar-gen2 clock-names list

The bindings have been updated to support two clocks.
Add a clock-names list in the device tree with fck in it.

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20210224115146.9131-2-aford173@gmail.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>