[][MAC80211][WiFi6][mt76][Remove redundant argument in add_beacon function]

[Description]
Remove redundant argument "changed".

[Release-log]
N/A

Change-Id: Ia47d6ba5f9881fa54d481c8e6e15829091b89806
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/8590290
1 file changed