NET: MIPS: Lantiq: Non existing PHY was not handled gracefully

NET: MIPS: Lantiq: Non existing PHY was not handled gracefully

The code blindly assumed that that a PHY device was present causing a BadVA.
In addition the driver should not fail to load incase no PHY was found.
Instead we print the following line and continue with no attached PHY.

   etop: mdio probe failed

Signed-off-by: John Crispin <blogic@openwrt.org>
Acked-by: David S. Miller <davem@davemloft.net>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3274/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>