net: pcs: mtk-usxgmii: fix usxgmii link flapping the mtk way

For the USXGMII link‑flap issue, remove statements that are already
executed inside mtk_usxgmii_pcs_config().

Author: bcchen28411

drivers/net/pcs/pcs-mtk-usxgmii.c

@@ -390,8 +390,6 @@ static void mtk_usxgmii_pcs_link_up(struct phylink_pcs *pcs, unsigned int neg_mo
 		return;
 
 	mtk_usxgmii_pcs_config(pcs, neg_mode, interface, NULL, false);
-	phy_reset(mpcs->xfi_tphy);
-	phy_set_mode_ext(mpcs->xfi_tphy, PHY_MODE_ETHERNET, interface);
 }
 
 static int mtk_usxgmii_pcs_enable(struct phylink_pcs *pcs)