wifi: Modify for SU 7668 USB Dongle support

Test: pass

Change-Id: I0b87b16974d14061575766aa2f4a94d2b51751b4
CR-Id: AUTO00014958
Signed-off-by: Shengxi Xu <shengxi.xu@mediatek.com>
Reviewed-on: http://gerrit.mediatek.inc:8080/1447837
CheckPatch: Check Patch <srv_checkpatch@mediatek.com>
Reviewed-by: Jiehang Zheng <jiehang.zheng@mediatek.com>
Tested-by: Jiehang Zheng <jiehang.zheng@mediatek.com>