[][Fix mt7981 upgrade plaform.sh typo issue]

[Description]
Fix mt7981 upgrade plaform.sh typo issue

[Release-log]
N/A

Change-Id: Ic2549c23614583932e8518c2e36a1045629208d9
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/5492024
1 file changed