[][kernel][MT7988][dsa][phy][coverity scan fix]

[Description]
Fix Converity scan error.

[Release-log]
N/A

Change-Id: I755ce2ea040b093a993a1859ff3a009c64ae6bed
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/6838042
1 file changed