net: stmmac: Delete dead code for MDIO registration

This code is no longer used, the logging function was changed by commit
fbca1647 ("net: stmmac: Use the right logging function in stmmac_mdio_register").
It was previously showing information about the type of the IRQ, if it's
polled, ignored or a normal interrupt. As we don't want information loss,
I have moved this code to phy_attached_print().

Fixes: fbca1647 ("net: stmmac: Use the right logging function in stmmac_mdio_register")
Signed-off-by: Romain Perier <romain.perier@collabora.com>
Signed-off-by: David S. Miller <davem@davemloft.net>