Fix the following make W=1 kernel build warning:

 drivers/net/mdio.c:95: warning: expecting prototype for mdio_link_ok(). Prototype was for mdio45_links_ok() instead
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>