mt76: mt7921s: fix bus hang with wrong privilege

Accroding to chip hw flow, mt7921s need to re-acquire privilege
again before normal running. Otherwise, the bus may be stuck in
an abnormal status.

Tested-by: Leon Yen <Leon.Yen@mediatek.com>
Co-developed-by: Eric-SY Chang <Eric-SY.Chang@mediatek.com>
Signed-off-by: Eric-SY Chang <Eric-SY.Chang@mediatek.com>
Co-developed-by: YN Chen <YN.Chen@mediatek.com>
Signed-off-by: YN Chen <YN.Chen@mediatek.com>
Signed-off-by: Deren Wu <deren.wu@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>