ath10k: add max_tx_power for QCA6174 WLAN.RM.2.0 firmware

BugLink: https://bugs.launchpad.net/bugs/1736317

QCA6174 WLAN.RM.2.0 firmware uses max_tx_power instead of using max_reg_power
to set transmission power. The tx power was about -50dbm, after applying this
change, it become -32dbm.
Signed-off-by: Alan Liu <alanliu@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>
(cherry picked from commit 513527c8)
Signed-off-by: Shrirang Bagul <shrirang.bagul@canonical.com>
Acked-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
Acked-by: Kai Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/net/wireless/ath/ath10k/wmi.c

@@ -1573,6 +1573,7 @@ void ath10k_wmi_put_wmi_channel(struct wmi_channel *ch,
 	ch->max_power = arg->max_power;
 	ch->reg_power = arg->max_reg_power;
 	ch->antenna_max = arg->max_antenna_gain;
+	ch->max_tx_power = arg->max_power;
 
 	/* mode & flags share storage */
 	ch->mode = arg->mode;

drivers/net/wireless/ath/ath10k/wmi.h

@@ -1732,6 +1732,7 @@ struct wmi_channel {
 		__le32 reginfo1;
 		struct {
 			u8 antenna_max;
+			u8 max_tx_power;
 		} __packed;
 	} __packed;
 } __packed;