tsnep: Fix tsnep_tx_unmap() error path usage

If tsnep_tx_map() fails, then tsnep_tx_unmap() shall start at the write
index like tsnep_tx_map(). This is different to the normal operation.
Thus, add an additional parameter to tsnep_tx_unmap() to enable start at
different positions for successful TX and failed TX.

Fixes: 403f69bb ("tsnep: Add TSN endpoint Ethernet MAC driver")
Signed-off-by: Gerhard Engleder <gerhard@engleder-embedded.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/engleder/tsnep_main.c

@@ -340,14 +340,14 @@ static int tsnep_tx_map(struct sk_buff *skb, struct tsnep_tx *tx, int count)
 	return 0;
 }
 
-static void tsnep_tx_unmap(struct tsnep_tx *tx, int count)
+static void tsnep_tx_unmap(struct tsnep_tx *tx, int index, int count)
 {
 	struct device *dmadev = tx->adapter->dmadev;
 	struct tsnep_tx_entry *entry;
 	int i;
 
 	for (i = 0; i < count; i++) {
-		entry = &tx->entry[(tx->read + i) % TSNEP_RING_SIZE];
+		entry = &tx->entry[(index + i) % TSNEP_RING_SIZE];
 
 		if (entry->len) {
 			if (i == 0)
@@ -395,7 +395,7 @@ static netdev_tx_t tsnep_xmit_frame_ring(struct sk_buff *skb,
 
 	retval = tsnep_tx_map(skb, tx, count);
 	if (retval != 0) {
-		tsnep_tx_unmap(tx, count);
+		tsnep_tx_unmap(tx, tx->write, count);
 		dev_kfree_skb_any(entry->skb);
 		entry->skb = NULL;
 
@@ -464,7 +464,7 @@ static bool tsnep_tx_poll(struct tsnep_tx *tx, int napi_budget)
 		if (skb_shinfo(entry->skb)->nr_frags > 0)
 			count += skb_shinfo(entry->skb)->nr_frags;
 
-		tsnep_tx_unmap(tx, count);
+		tsnep_tx_unmap(tx, tx->read, count);
 
 		if ((skb_shinfo(entry->skb)->tx_flags & SKBTX_IN_PROGRESS) &&
 		    (__le32_to_cpu(entry->desc_wb->properties) &