wifi: mt76: mt7921: fix wrong 6Ghz power type

To avoid using incorrect 6g power settings after disconnection,
it should to update back to the default state when disconnected.

Fixes: 51ba0e3a ("wifi: mt76: mt7921: add 6GHz power type support for clc")
Signed-off-by: Ming Yen Hsieh <mingyen.hsieh@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>