wifi: rtw88: add mutex when set regulatory and get Tx power table

Applying regulatory and getting Tx power table will access hal
data, it should hold rtwdev::mutex to avoid hal data changed during
setting flow.

Signed-off-by: Chih-Kang Chang <gary.chang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220809084107.38137-3-pkshih@realtek.com