Revert "ARM64: DTS: meson-gxbb: switch ethernet to real clock"

This reverts commit f3abd629, which caused a build regression:

arch/arm64/boot/dts/amlogic/meson-gxbb.dtsi:48:41: fatal error: dt-bindings/clock/gxbb-clkc.h: No such file or directory

We should apply this patch one merge window later, once the clk branch
is merged as well.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>