net: ethernet: mtk_ppe: fix possible NULL pointer dereference in mtk_flow_get_wdma_info

odev pointer can be NULL in mtk_flow_offload_replace routine according
to the flower action rules. Fix possible NULL pointer dereference in
mtk_flow_get_wdma_info.

Fixes: a333215e ("net: ethernet: mtk_eth_soc: implement flow offloading to WED devices")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://lore.kernel.org/r/4e1685bc4976e21e364055f6bee86261f8f9ee93.1658137753.git.lorenzo@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mediatek/mtk_ppe_offload.c

@@ -93,6 +93,9 @@ mtk_flow_get_wdma_info(struct net_device *dev, const u8 *addr, struct mtk_wdma_i
 	};
 	struct net_device_path path = {};
 
+	if (!ctx.dev)
+		return -ENODEV;
+
 	memcpy(ctx.daddr, addr, sizeof(ctx.daddr));
 
 	if (!IS_ENABLED(CONFIG_NET_MEDIATEK_SOC_WED))