net: stmmac: Use the right logging function in stmmac_mdio_register

Currently, the function stmmac_mdio_register() is only used by
stmmac_dvr_probe() from stmmac_main.c, in order to register the MDIO bus
and probe information about the PHY. As this function is called before
calling register_netdev(), all messages logged from stmmac_mdio_register
are prefixed by "(unnamed net_device)". The goal of netdev_info or
netdev_err is to dump useful infos about a net_device, when this data
structure is partially initialized, there is no point for using these
functions.

This commit fixes the issue by replacing all netdev_*() by the
corresponding dev_*() function for logging. The last netdev_info is
replaced by phy_attached_info(), as a valid phydev can be used at this
point.

Signed-off-by: Romain Perier <romain.perier@collabora.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>