mt76: mt7921s: fix suspend error with enlarging mcu timeout value

Fix the false positive suspend error that may occur on mt7921s
with enlarging mcu timeout value.

The reason why we have to enlarge mcu timeout from HZ / 3 to HZ is
we should consider the additional overhead caused by running
concurrently with btmtksdio (a MT7921 bluetooth SDIO driver) that
would compete for the same SDIO bus in process context to complete
the suspend procedure.

Fixes: 48fab5bb

 ("mt76: mt7921: introduce mt7921s support")
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>