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>
diff --git a/drivers/iio/humidity/dht11.c b/drivers/iio/humidity/dht11.c
index 343d26a..bb5ad57 100644
--- a/drivers/iio/humidity/dht11.c
+++ b/drivers/iio/humidity/dht11.c
@@ -63,6 +63,7 @@
 	int				irq;
 
 	struct completion		completion;
+	/* The iio sysfs interface doesn't prevent concurrent reads: */
 	struct mutex			lock;
 
 	s64				timestamp;