iio: light: tcs3414: use iio helper function to guarantee direct mode

Replace the code that guarantees the device stays in direct mode
with iio_device_claim_direct_mode() which does same.  This allows
removal of an unused lock in the device private global data.

Also prevents a possible race around a buffer being enabled whilst
a read is going on.
Signed-off-by: NAlison Schofield <amsfield22@gmail.com>
Cc: Daniel Baluta <daniel.baluta@gmail.com>
Acked-by: NPeter Meerwald-Stadler <pmeerw@pmeerw.net>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>

drivers/iio/light/tcs3414.c

@@ -53,7 +53,6 @@
 
 struct tcs3414_data {
 	struct i2c_client *client;
-	struct mutex lock;
 	u8 control;
 	u8 gain;
 	u8 timing;
@@ -134,16 +133,16 @@ static int tcs3414_read_raw(struct iio_dev *indio_dev,
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
-		if (iio_buffer_enabled(indio_dev))
-			return -EBUSY;
-		mutex_lock(&data->lock);
+		ret = iio_device_claim_direct_mode(indio_dev);
+		if (ret)
+			return ret;
 		ret = tcs3414_req_data(data);
 		if (ret < 0) {
-			mutex_unlock(&data->lock);
+			iio_device_release_direct_mode(indio_dev);
 			return ret;
 		}
 		ret = i2c_smbus_read_word_data(data->client, chan->address);
-		mutex_unlock(&data->lock);
+		iio_device_release_direct_mode(indio_dev);
 		if (ret < 0)
 			return ret;
 		*val = ret;
@@ -288,7 +287,6 @@ static int tcs3414_probe(struct i2c_client *client,
 	data = iio_priv(indio_dev);
 	i2c_set_clientdata(client, indio_dev);
 	data->client = client;
-	mutex_init(&data->lock);
 
 	indio_dev->dev.parent = &client->dev;
 	indio_dev->info = &tcs3414_info;