net: stmmac: clean up passing fwnode to phylink

Move the initialisation of the fwnode variable closer to its use
site, rather than scattered throughout stmmac_phy_setup().

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/E1qZAXD-005pTv-TN@rmk-PC.armlinux.org.uk


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