net: meson: fixup g12a glue ephy id

The phy id chosen by Amlogic is incorrectly set in the mdio mux and
does not match the phy driver.

It was not detected before because DT forces the use the correct driver
for the internal PHY.

Fixes: 70904251 ("net: phy: add amlogic g12a mdio mux support")
Reported-by: Qi Duan <qi.duan@amlogic.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: David S. Miller <davem@davemloft.net>