net: txgbe: fix null pointer to pcs

For 1000BASE-X or SGMII interface mode, the PCS also need to be selected.
Only return null pointer when there is a copper NIC with external PHY.

Fixes: 02b2a6f ("net: txgbe: support copper NIC with external PHY")
Signed-off-by: Jiawen Wu <jiawenwu@trustnetic.com>
Link: https://patch.msgid.link/20241115073508.1130046-1-jiawenwu@trustnetic.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Jiawen Wu

drivers/net/ethernet/wangxun/txgbe/txgbe_phy.c

@@ -162,7 +162,7 @@ static struct phylink_pcs *txgbe_phylink_mac_select(struct phylink_config *confi
 	struct wx *wx = phylink_to_wx(config);
 	struct txgbe *txgbe = wx->priv;
 
-	if (interface == PHY_INTERFACE_MODE_10GBASER)
+	if (wx->media_type != sp_media_copper)
 		return &txgbe->xpcs->pcs;
 
 	return NULL;