net: phy: Correct function name mdiobus_register_board_info() in comment

Fix the following make W=1 kernel build warning:

 drivers/net/phy/mdio-boardinfo.c:63: warning: expecting prototype for mdio_register_board_info(). Prototype was for mdiobus_register_board_info() instead

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>