wifi: mt76: mt7996: disable WFDMA Tx/Rx during SER recovery

Stop WFDMA transaction to avoid potential unexpected issue while doing
system recovery.

Signed-off-by: Bo Jiao <Bo.Jiao@mediatek.com>
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>