hwmon: (adm1029) Add a comment for locking mutex

Checkpatch complains that mutex does not have any comment.
This patch fix that.
Signed-off-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/adm1029.c

@@ -108,7 +108,7 @@ static const u8 ADM1029_REG_FAN_DIV[] = {
 
 struct adm1029_data {
 	struct i2c_client *client;
-	struct mutex update_lock;
+	struct mutex update_lock; /* protect register access */
 	char valid;		/* zero until following fields are valid */
 	unsigned long last_updated;	/* in jiffies */