net: ethernet: lantiq_etop: fix double free in detach

The number of the currently released descriptor is never incremented
which results in the same skb being released multiple times.

Fixes: 504d4721 ("MIPS: Lantiq: Add ethernet driver")
Reported-by: Joe Perches <joe@perches.com>
Closes: https://lore.kernel.org/all/fc1bf93d92bb5b2f99c6c62745507cc22f3a7b2d.camel@perches.com/Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20240708205826.5176-1-olek2@wp.plSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/lantiq_etop.c

@@ -217,9 +217,9 @@ ltq_etop_free_channel(struct net_device *dev, struct ltq_etop_chan *ch)
 	if (ch->dma.irq)
 		free_irq(ch->dma.irq, priv);
 	if (IS_RX(ch->idx)) {
-		int desc;
+		struct ltq_dma_channel *dma = &ch->dma;
 
-		for (desc = 0; desc < LTQ_DESC_NUM; desc++)
+		for (dma->desc = 0; dma->desc < LTQ_DESC_NUM; dma->desc++)
 			dev_kfree_skb_any(ch->skb[ch->dma.desc]);
 	}
 }