hwmon: (occ) Lock mutex in shutdown to prevent race with occ_active

Unbinding the driver or removing the parent device at the same time
as using the OCC active sysfs file can cause the driver to unregister
the hwmon device twice. Prevent this by locking the occ mutex in the
shutdown function.
Signed-off-by: NEddie James <eajames@linux.ibm.com>
Link: https://lore.kernel.org/r/20220606185455.21126-1-eajames@linux.ibm.comSigned-off-by: NGuenter Roeck <linux@roeck-us.net>

drivers/hwmon/occ/common.c

@@ -1228,10 +1228,15 @@ EXPORT_SYMBOL_GPL(occ_setup);
 
 void occ_shutdown(struct occ *occ)
 {
+	mutex_lock(&occ->lock);
+
 	occ_shutdown_sysfs(occ);
 
 	if (occ->hwmon)
 		hwmon_device_unregister(occ->hwmon);
+	occ->hwmon = NULL;
+
+	mutex_unlock(&occ->lock);
 }
 EXPORT_SYMBOL_GPL(occ_shutdown);