arm64: dts: amlogic: meson-gxm-s912-libretech-pc: remove unused pinctrl-names from phy node

Fixes the following bindings check error:
phy@78000: 'pinctrl-0' is a dependency of 'pinctrl-names'

Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://lore.kernel.org/r/20230207-b4-amlogic-bindings-fixups-v2-v1-8-93b7e50286e7@linaro.org


Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>