cpmac: use after free

The original code dereferenced "cpmac_mii" after calling
"mdiobus_free(cpmac_mii);"

Signed-off-by: Dan Carpenter <error27@gmail.com>
Reviewed-by: Jiri Pirko <jpirko@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>