net: dsa: lantiq_gswip: support standard MDIO node name

net: dsa: lantiq_gswip: support standard MDIO node name

Instead of matching against the child node's compatible string also
support locating the node of the device tree node of the MDIO bus
in the standard way by referencing the node name ("mdio").

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Reviewed-by: Hauke Mehrtens <hauke@hauke-m.de>
Link: https://patch.msgid.link/5a9a3d659ef0d8b7eca37fb69ec87ff5a3192820.1756520811.git.daniel@makrotopia.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>