net: bgmac: fix reversed check for MII registration error

It was failing on successful registration returning meaningless errors.
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Fixes: 55954f3b ("net: ethernet: bgmac: move BCMA MDIO Phy code into a separate file")
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bgmac-bcma.c

@@ -159,7 +159,7 @@ static int bgmac_probe(struct bcma_device *core)
 
 	if (!bgmac_is_bcm4707_family(core)) {
 		mii_bus = bcma_mdio_mii_register(core, bgmac->phyaddr);
-		if (!IS_ERR(mii_bus)) {
+		if (IS_ERR(mii_bus)) {
 			err = PTR_ERR(mii_bus);
 			goto err;
 		}