net: ethernet: ti: cpsw_ethtool: fix ethtool ring param set

Fix ability to set RX descriptor number, the reason - initially
"tx_max_pending" was set incorrectly, but the issue appears after
adding sanity check, so fix is for "sanity" patch.

Fixes: 37e2d99b ("ethtool: Ensure new ring parameters are within bounds during SRINGPARAM")
Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/ti/cpsw_ethtool.c

@@ -643,7 +643,7 @@ void cpsw_get_ringparam(struct net_device *ndev,
 	struct cpsw_common *cpsw = priv->cpsw;
 
 	/* not supported */
-	ering->tx_max_pending = 0;
+	ering->tx_max_pending = cpsw->descs_pool_size - CPSW_MAX_QUEUES;
 	ering->tx_pending = cpdma_get_num_tx_descs(cpsw->dma);
 	ering->rx_max_pending = cpsw->descs_pool_size - CPSW_MAX_QUEUES;
 	ering->rx_pending = cpdma_get_num_rx_descs(cpsw->dma);