amd-xgbe: Set the MII control width for the MAC interface

When running in SGMII mode at speeds below 1000Mbps, the auto-negotition
control register must set the MII control width for the MAC interface
to be 8-bits wide.  By default the width is 4-bits.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-mdio.c b/drivers/net/ethernet/amd/xgbe/xgbe-mdio.c
index 8068491..2222bbf8 100644
--- a/drivers/net/ethernet/amd/xgbe/xgbe-mdio.c
+++ b/drivers/net/ethernet/amd/xgbe/xgbe-mdio.c
@@ -982,6 +982,8 @@ static void xgbe_an37_init(struct xgbe_prv_data *pdata)
 		break;
 	}
 
+	reg |= XGBE_AN_CL37_MII_CTRL_8BIT;
+
 	XMDIO_WRITE(pdata, MDIO_MMD_VEND2, MDIO_VEND2_AN_CTRL, reg);
 
 	netif_dbg(pdata, link, pdata->netdev, "CL37 AN (%s) initialized\n",