[][Fix coverity scan check errors in mtk eth driver]

[Description]
Fix coverity scan check errors in mtk eth driver

[Release-log]
N/A

Change-Id: Idd57117afcc0478c107ef0e683a4993eb80221c0
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/5108909
diff --git a/target/linux/mediatek/files-5.4/drivers/net/ethernet/mediatek/mtk_eth_soc.h b/target/linux/mediatek/files-5.4/drivers/net/ethernet/mediatek/mtk_eth_soc.h
index b8c0728..3922064 100755
--- a/target/linux/mediatek/files-5.4/drivers/net/ethernet/mediatek/mtk_eth_soc.h
+++ b/target/linux/mediatek/files-5.4/drivers/net/ethernet/mediatek/mtk_eth_soc.h
@@ -1221,7 +1221,7 @@
  * @hw_stats:		Packet statistics counter
  */
 struct mtk_mac {
-	int				id;
+	unsigned int			id;
 	phy_interface_t			interface;
 	unsigned int			mode;
 	int				speed;