net: mdiobus: fix fwnode_mdbiobus_register() fallback case

The fallback case of fwnode_mdbiobus_register()
(relevant for !CONFIG_FWNODE_MDIO) was defined with wrong
argument name, causing a compilation error. Fix that.

Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>