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>