iio: dht11: add comment to make checkpatch.pl --strict happy

Explain why the driver needs a mutex.
Signed-off-by: Harald Geyer <harald@ccbib.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/humidity/dht11.c

@@ -63,6 +63,7 @@ struct dht11 {
 	int				irq;
 
 	struct completion		completion;
+	/* The iio sysfs interface doesn't prevent concurrent reads: */
 	struct mutex			lock;
 
 	s64				timestamp;