wifi: mt76: mt7921s: fix potential hung tasks during chip recovery

During chip recovery (e.g. chip reset), there is a possible situation that
kernel worker reset_work is holding the lock and waiting for kernel thread
stat_worker to be parked, while stat_worker is waiting for the release of
the same lock.
It causes a deadlock resulting in the dumping of hung tasks messages and
possible rebooting of the device.

This patch prevents the execution of stat_worker during the chip recovery.

Signed-off-by: Leon Yen <leon.yen@mediatek.com>
Signed-off-by: Ming Yen Hsieh <MingYen.Hsieh@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>