net: stmmac: dwmac-sun8i: use return val of readl_poll_timeout()

When readl_poll_timeout() timeout, we'd better directly use its return
value.

Before this patch:
[    2.145528] dwmac-sun8i: probe of 4500000.ethernet failed with error -14

After this patch:
[    2.138520] dwmac-sun8i: probe of 4500000.ethernet failed with error -110
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/dwmac-sun8i.c

@@ -756,7 +756,7 @@ static int sun8i_dwmac_reset(struct stmmac_priv *priv)
 
 	if (err) {
 		dev_err(priv->device, "EMAC reset timeout\n");
-		return -EFAULT;
+		return err;
 	}
 	return 0;
 }