Bluetooth: mt7921s: fix bus hang with wrong privilege

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

Fixes: c603bf1f ("Bluetooth: btmtksdio: add MT7921s Bluetooth support")
Co-developed-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Mark Chen <mark-yw.chen@mediatek.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>