net: mv643xx_eth: potential NULL dereference in probe()

We assume that "mp->phy" can be NULL a couple lines before the
dereference.

Fixes: 1cce16d3 ('net: mv643xx_eth: Add missing phy_addr_set in DT mode')
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Acked-by: NSebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Acked-by: NJason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/marvell/mv643xx_eth.c

@@ -2890,7 +2890,8 @@ static int mv643xx_eth_probe(struct platform_device *pdev)
 					 PHY_INTERFACE_MODE_GMII);
 		if (!mp->phy)
 			err = -ENODEV;
-		phy_addr_set(mp, mp->phy->addr);
+		else
+			phy_addr_set(mp, mp->phy->addr);
 	} else if (pd->phy_addr != MV643XX_ETH_PHY_NONE) {
 		mp->phy = phy_scan(mp, pd->phy_addr);