[][openwrt][mt7988][eth][Fix coverity issue for Ethernet driver]

[Description]
Add Ethernet driver changes to fix coverity issue.

If without this patch, the procedure of port link setting
might run into undefined behavior due to uninitialized
variable.

[Release-log]
N/A


Change-Id: I2134e038742a3028112ce48544d6058bb302bb73
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/7928489
1 file changed