TI DaVinci EMAC: Fix MDIO bus frequency configuration

There was a typo in "if condition" checking for validity of MDIO
bus frequency passed as part of platform data. Bitwise AND was
being used instead of a Logical AND.

Tested on: DM6467 EVM

Signed-off-by: Nageswari Srinivasan <nageswari@ti.com>
Acked-by: Anant Gole <anantgole@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>