ath6kl: Avoid null ptr dereference while printing reg domain pair

Return value of ath6kl_get_regpair() is stored in 'regpair' in
ath6kl_wmi_regdomain_event() func and it's directly accessed
in the debug prints without checking for NULL value. There are
situation to get NULL pointer as a return value from
ath6kl_get_regpair() func. Fix this.

Found this on code review.
Signed-off-by: Raja Mani <rmani@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/ath6kl/wmi.c

@@ -936,8 +936,12 @@ static void ath6kl_wmi_regdomain_event(struct wmi *wmi, u8 *datap, int len)
 
 		regpair = ath6kl_get_regpair((u16) reg_code);
 		country = ath6kl_regd_find_country_by_rd((u16) reg_code);
-		ath6kl_dbg(ATH6KL_DBG_WMI, "Regpair used: 0x%0x\n",
-			   regpair->regDmnEnum);
+		if (regpair)
+			ath6kl_dbg(ATH6KL_DBG_WMI, "Regpair used: 0x%0x\n",
+				   regpair->regDmnEnum);
+		else
+			ath6kl_warn("Regpair not found reg_code 0x%0x\n",
+				    reg_code);
 	}
 
 	if (country && wmi->parent_dev->wiphy_registered) {