wifi: mt76: mt7921: fix antenna signal are way off in monitor mode

Group 3 in RxD is disabled in monitor mode. We should use the group 5 in
RxD instead to fix antenna signal way off issue, e.g we would see the
incorrect antenna signal value in wireshark. On the other hand, Group 5
wouldn't be used in STA or AP mode, so the patch shouldn't cause any
harm to those modes.

Fixes: cbaa0a40 ("mt76: mt7921: fix up the monitor mode")
Reported-by: Adrian Granados <agranados@gmail.com>
Co-developed-by: Deren Wu <deren.wu@mediatek.com>
Signed-off-by: Deren Wu <deren.wu@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>