rtw88: 8821c: add false alarm statistics

False alarm statistics can be used to adjust the RX gain. This
helps the driver to adapt to different circumstances.

Implement rtw_chip_ops::false_alarm_statistics() for 8821c.

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Tzu-En Huang <tehuang@realtek.com>
Signed-off-by: Yan-Hsuan Chuang <yhchuang@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200616091625.26489-7-yhchuang@realtek.com