net: cpmac: remove cpmac_config

cpmac_config() refuses changing the base address parameter, and ignores
all other parameters, which means that it is pretty useless as it is, so
let's remove it.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>