ath10k: replace config_enabled() with IS_REACHABLE()

Commit 97f2645f ("tree-wide: replace config_enabled() with
IS_ENABLED()") mostly did away with config_enabled().

This is one of the postponed TODO items as config_enabled() is used
for a tristate option here.  Theoretically, config_enabled() is
equivalent to IS_BUILTIN(), but I guess IS_REACHABLE() is the best
fit for this case because both CONFIG_HWMON and CONFIG_ATH10K are
tristate.
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: NKalle Valo <kvalo@qca.qualcomm.com>

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

@@ -192,7 +192,7 @@ int ath10k_thermal_register(struct ath10k *ar)
 
 	/* Avoid linking error on devm_hwmon_device_register_with_groups, I
 	 * guess linux/hwmon.h is missing proper stubs. */
-	if (!config_enabled(CONFIG_HWMON))
+	if (!IS_REACHABLE(CONFIG_HWMON))
 		return 0;
 
 	hwmon_dev = devm_hwmon_device_register_with_groups(ar->dev,