net: airoha: Move ndesc initialization at end of airoha_qdma_init_tx()

If queue entry list allocation fails in airoha_qdma_init_tx_queue routine,
airoha_qdma_cleanup_tx_queue() will trigger a NULL pointer dereference
accessing the queue entry array. The issue is due to the early ndesc
initialization in airoha_qdma_init_tx_queue(). Fix the issue moving ndesc
initialization at end of airoha_qdma_init_tx routine.

Fixes: 3f47e67 ("net: airoha: Add the capability to consume out-of-order DMA tx descriptors")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20260417-airoha_qdma_cleanup_tx_queue-fix-net-v4-1-e04bcc2c9642@kernel.org
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: LorenzoBianconi

drivers/net/ethernet/airoha/airoha_eth.c

@@ -978,27 +978,27 @@ static int airoha_qdma_init_tx_queue(struct airoha_queue *q,
 	dma_addr_t dma_addr;
 
 	spin_lock_init(&q->lock);
-	q->ndesc = size;
 	q->qdma = qdma;
 	q->free_thr = 1 + MAX_SKB_FRAGS;
 	INIT_LIST_HEAD(&q->tx_list);
 
-	q->entry = devm_kzalloc(eth->dev, q->ndesc * sizeof(*q->entry),
+	q->entry = devm_kzalloc(eth->dev, size * sizeof(*q->entry),
 				GFP_KERNEL);
 	if (!q->entry)
 		return -ENOMEM;
 
-	q->desc = dmam_alloc_coherent(eth->dev, q->ndesc * sizeof(*q->desc),
+	q->desc = dmam_alloc_coherent(eth->dev, size * sizeof(*q->desc),
 				      &dma_addr, GFP_KERNEL);
 	if (!q->desc)
 		return -ENOMEM;
 
-	for (i = 0; i < q->ndesc; i++) {
+	for (i = 0; i < size; i++) {
 		u32 val = FIELD_PREP(QDMA_DESC_DONE_MASK, 1);
 
 		list_add_tail(&q->entry[i].list, &q->tx_list);
 		WRITE_ONCE(q->desc[i].ctrl, cpu_to_le32(val));
 	}
+	q->ndesc = size;
 
 	/* xmit ring drop default setting */
 	airoha_qdma_set(qdma, REG_TX_RING_BLOCKING(qid),