net: tn40xx: prepare tn40xx driver to find phy of the TN9510 card

Prepare the tn40xx driver to load for Tehuti TN9510 cards, which require
bit 3 in the register TN40_REG_MDIO_CMD_STAT to be set. The function of bit
3 is unclear, but may have something to do with the length of the preamble
in the MDIO communication. If bit 3 is not set, the PHY will not be found
when performing a scan for PHYs. Use the available tn40_mdio_set_speed
function which includes setting bit 3. Just move the function to before the
devm_mdio_register function, which scans the mdio bus for PHYs.

Signed-off-by: Hans-Frieder Vogt <hfdevel@gmx.net>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Link: https://patch.msgid.link/20250322-tn9510-v3a-v7-6-672a9a3d8628@gmx.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/tehuti/tn40_mdio.c

@@ -200,13 +200,13 @@ int tn40_mdiobus_init(struct tn40_priv *priv)
 		}
 	}
 
+	tn40_mdio_set_speed(priv, TN40_MDIO_SPEED_6MHZ);
 	ret = devm_mdiobus_register(&pdev->dev, bus);
 	if (ret) {
 		dev_err(&pdev->dev, "failed to register mdiobus %d %u %u\n",
 			ret, bus->state, MDIOBUS_UNREGISTERED);
 		goto err_swnodes_cleanup;
 	}
-	tn40_mdio_set_speed(priv, TN40_MDIO_SPEED_6MHZ);
 	return 0;
 
 err_swnodes_unregister: