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 <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/mediatek/mtk_wed.c

···
 					   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);