generic: mtk_eth_soc: don't crash if WO firmware is missing

Import patch to prevent crashes in case WO firmware is missing on devices
with only a single frontend (eg. MT7981+MT7976).

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

target/linux/generic/backport-5.15/733-v6.4-22-net-ethernet-mtk_eth_soc-fix-NULL-pointer-dereferenc.patch

@@ -0,0 +1,28 @@
+From 7c83e28f10830aa5105c25eaabe890e3adac36aa Mon Sep 17 00:00:00 2001
+From: Daniel Golle <daniel@makrotopia.org>
+Date: Tue, 9 May 2023 03:20:06 +0200
+Subject: [PATCH] net: ethernet: mtk_eth_soc: fix NULL pointer dereference
+
+Check for NULL pointer to avoid kernel crashing in case of missing WO
+firmware in case only a single WEDv2 device has been initialized, e.g. on
+MT7981 which can connect just one wireless frontend.
+
+Fixes: 86ce0d09e424 ("net: ethernet: mtk_eth_soc: use WO firmware for MT7981")
+Signed-off-by: Daniel Golle <daniel@makrotopia.org>
+Reviewed-by: Simon Horman <simon.horman@corigine.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ drivers/net/ethernet/mediatek/mtk_wed.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+--- a/drivers/net/ethernet/mediatek/mtk_wed.c
++++ b/drivers/net/ethernet/mediatek/mtk_wed.c
+@@ -647,7 +647,7 @@ __mtk_wed_detach(struct mtk_wed_device *
+ 					   BIT(hw->index), BIT(hw->index));
+ 	}
+
+-	if (!hw_list[!hw->index]->wed_dev &&
++	if ((!hw_list[!hw->index] || !hw_list[!hw->index]->wed_dev) &&
+ 	    hw->eth->dma_dev != hw->eth->dev)
+ 		mtk_eth_set_dma_device(hw->eth, hw->eth->dev);
+