[][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
3 files changed