r8169: Avoid duplicate sysfs entry creation error

When registering the MDIO bus for a r8169 device, we use the PCI B/D/F
specifier as a (seemingly) unique device identifier.
However the very same BDF number can be used on another PCI segment,
which makes the driver fail probing:

[ 27.544136] r8169 0002:07:00.0: enabling device (0000 -> 0003)
[ 27.559734] sysfs: cannot create duplicate filename '/class/mdio_bus/r8169-700'
....…
[ 27.684858] libphy: mii_bus r8169-700 failed to register
[ 27.695602] r8169: probe of 0002:07:00.0 failed with error -22

Add the segment number to the device name to make it more unique.

This fixes operation on an ARM N1SDP board, where two boards might be
connected together to form an SMP system, and all on-board devices show
up twice, just on different PCI segments.

Signed-off-by: Sayanta Pattanayak <sayanta.pattanayak@arm.com>
[Andre: expand commit message]
Signed-off-by: Andre Przywara <andre.przywara@arm.com>

drivers/net/ethernet/realtek/r8169_main.c

@@ -5086,7 +5086,8 @@ static int r8169_mdio_register(struct rtl8169_private *tp)
 	new_bus->priv = tp;
 	new_bus->parent = &pdev->dev;
 	new_bus->irq[0] = PHY_MAC_INTERRUPT;
-	snprintf(new_bus->id, MII_BUS_ID_SIZE, "r8169-%x", pci_dev_id(pdev));
+	snprintf(new_bus->id, MII_BUS_ID_SIZE, "r8169-%x-%x",
+		 pdev->bus->domain_nr, pci_dev_id(pdev));
 
 	new_bus->read = r8169_mdio_read_reg;
 	new_bus->write = r8169_mdio_write_reg;