net: mvneta: fix double free of txq->buf

clang static analysis reports this problem:

drivers/net/ethernet/marvell/mvneta.c:3465:2: warning:
  Attempt to free released memory
        kfree(txq->buf);
        ^~~~~~~~~~~~~~~

When mvneta_txq_sw_init() fails to alloc txq->tso_hdrs,
it frees without poisoning txq->buf.  The error is caught
in the mvneta_setup_txqs() caller which handles the error
by cleaning up all of the txqs with a call to
mvneta_txq_sw_deinit which also frees txq->buf.

Since mvneta_txq_sw_deinit is a general cleaner, all of the
partial cleaning in mvneta_txq_sw_deinit()'s error handling
is not needed.

Fixes: 2adb719 ("net: mvneta: Implement software TSO")
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: Tom Rix

drivers/net/ethernet/marvell/mvneta.c

@@ -3400,24 +3400,15 @@ static int mvneta_txq_sw_init(struct mvneta_port *pp,
 	txq->last_desc = txq->size - 1;
 
 	txq->buf = kmalloc_array(txq->size, sizeof(*txq->buf), GFP_KERNEL);
-	if (!txq->buf) {
-		dma_free_coherent(pp->dev->dev.parent,
-				  txq->size * MVNETA_DESC_ALIGNED_SIZE,
-				  txq->descs, txq->descs_phys);
+	if (!txq->buf)
 		return -ENOMEM;
-	}
 
 	/* Allocate DMA buffers for TSO MAC/IP/TCP headers */
 	txq->tso_hdrs = dma_alloc_coherent(pp->dev->dev.parent,
 					   txq->size * TSO_HEADER_SIZE,
 					   &txq->tso_hdrs_phys, GFP_KERNEL);
-	if (!txq->tso_hdrs) {
-		kfree(txq->buf);
-		dma_free_coherent(pp->dev->dev.parent,
-				  txq->size * MVNETA_DESC_ALIGNED_SIZE,
-				  txq->descs, txq->descs_phys);
+	if (!txq->tso_hdrs)
 		return -ENOMEM;
-	}
 
 	/* Setup XPS mapping */
 	if (txq_number > 1)