wifi: mt76: mt7915: fix WED TxS reporting

The previous commit forgot to remove a leftover check.

Fixes: 43eaa368 ("wifi: mt76: add PPDU based TxS support for WED device")
Reported-By: Sujuan Chen <sujuan.chen@mediatek.com>
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>