net: davinci: fix building davinci mdio code without CONFIG_OF

Test-building this driver on targets without CONFIG_OF revealed a build
failure:

drivers/net/ethernet/ti/davinci_mdio.c: In function 'davinci_mdio_probe':
drivers/net/ethernet/ti/davinci_mdio.c:380:9: error: implicit declaration of function 'davinci_mdio_probe_dt'; did you mean 'davinci_mdio_probe'? [-Werror=implicit-function-declaration]

This adjusts the #ifdef logic in the driver to make it build in
all configurations.

Fixes: 2652113f

 ("net: ethernet: ti: Allow most drivers with COMPILE_TEST")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>