Bluetooth: btmtksdio: update register CSDIOCSR operation

That is a preliminary patch to introduce mt7921s support.

Update register CSDIOCSR operation that is suggested from the vendor
driver and is compatible to the all devices.

Co-developed-by: Mark-yw Chen <mark-yw.chen@mediatek.com>
Signed-off-by: Mark-yw Chen <mark-yw.chen@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>