net: ethernet: mtk_eth_soc: fix memory corruption during fq dma init

The loop responsible for allocating up to MTK_FQ_DMA_LENGTH buffers must
only touch as many descriptors, otherwise it ends up corrupting unrelated
memory. Fix the loop iteration count accordingly.

Fixes: c57e558 ("net: ethernet: mtk_eth_soc: handle dma buffer size soc specific")
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20241015081755.31060-1-nbd@nbd.name
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/ethernet/mediatek/mtk_eth_soc.c

@@ -1311,7 +1311,7 @@ static int mtk_init_fq_dma(struct mtk_eth *eth)
 		if (unlikely(dma_mapping_error(eth->dma_dev, dma_addr)))
 			return -ENOMEM;
 
-		for (i = 0; i < cnt; i++) {
+		for (i = 0; i < len; i++) {
 			struct mtk_tx_dma_v2 *txd;
 
 			txd = eth->scratch_ring + (j * MTK_FQ_DMA_LENGTH + i) * soc->tx.desc_size;