net: stmmac: Check if CBS is supported before configuring

Check if CBS is currently supported before trying to configure it in HW.

Cc: Joao Pinto <jpinto@synopsys.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c

@@ -301,6 +301,8 @@ static int tc_setup_cbs(struct stmmac_priv *priv,
 	/* Queue 0 is not AVB capable */
 	if (queue <= 0 || queue >= tx_queues_count)
 		return -EINVAL;
+	if (!priv->dma_cap.av)
+		return -EOPNOTSUPP;
 	if (priv->speed != SPEED_100 && priv->speed != SPEED_1000)
 		return -EOPNOTSUPP;