net: dwmac-sun8i: Use parsed internal PHY address instead of 1

While the MDIO address of the internal PHY on Allwinner sun8i chips is
generally 1, of_mdio_parse_addr is used to cleanly parse the address
from the device-tree instead of hardcoding it.

A commit reworking the code ditched the parsed value and hardcoded the
value 1 instead, which didn't really break anything but is more fragile
and not future-proof.

Restore the initial behavior using the parsed address returned from the
helper.

Fixes: 634db83b ("net: stmmac: dwmac-sun8i: Handle integrated/external MDIOs")
Signed-off-by: Paul Kocialkowski <paulk@sys-base.io>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Corentin LABBE <clabbe.montjoie@gmail.com>
Tested-by: Corentin LABBE <clabbe.montjoie@gmail.com>
Link: https://patch.msgid.link/20250519164936.4172658-1-paulk@sys-base.io


Signed-off-by: Jakub Kicinski <kuba@kernel.org>