Bluetooth: mt7921s: fix firmware coredump retrieve

According to the MCU firmware behavior, as the driver is aware of the
notification of the interrupt source FW_MAILBOX_INT that shows the MCU
completed delivered a core dump piece to the host, the driver must
acknowledge the MCU with the register PH2DSM0R bit PH2DSM0R_DRIVER_OWN
to notify the MCU to handle the next core dump piece.

Fixes: db57b625 ("Bluetooth: btmtksdio: add support of processing firmware coredump and log")
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>