ath10k: fix build error when hwmon is off

kbuild reported a linking error:

ERROR: "devm_hwmon_device_register_with_groups"
[drivers/net/wireless/ath/ath10k/ath10k_core.ko] undefined!

Fix it by returning early and letting the compiler to optimise out the function
call.
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

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

@@ -213,6 +213,11 @@ int ath10k_thermal_register(struct ath10k *ar)
 	if (ar->wmi.op_version != ATH10K_FW_WMI_OP_VERSION_10_2_4)
 		return 0;
 
+	/* Avoid linking error on devm_hwmon_device_register_with_groups, I
+	 * guess linux/hwmon.h is missing proper stubs. */
+	if (!config_enabled(HWMON))
+		return 0;
+
 	hwmon_dev = devm_hwmon_device_register_with_groups(ar->dev,
 							   "ath10k_hwmon", ar,
 							   ath10k_hwmon_groups);