staging: iio: ad9832: replace mlock with driver private lock

The IIO subsystem is redefining iio_dev->mlock to be used by
the IIO core only for protecting device operating mode changes.
ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.

In this driver, mlock was being used to protect hardware state
changes.  Replace it with a lock in the devices global data.
Signed-off-by: Alison Schofield <amsfield22@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/frequency/ad9832.c

@@ -84,6 +84,7 @@
  * @freq_msg:		tuning word spi message
  * @phase_xfer:		tuning word spi transfer
  * @phase_msg:		tuning word spi message
+ * @lock		protect sensor state
  * @data:		spi transmit buffer
  * @phase_data:		tuning word spi transmit buffer
  * @freq_data:		tuning word spi transmit buffer
@@ -103,6 +104,7 @@ struct ad9832_state {
 	struct spi_message		freq_msg;
 	struct spi_transfer		phase_xfer[2];
 	struct spi_message		phase_msg;
+	struct mutex			lock;	/* protect sensor state */
 	/*
 	 * DMA (thus cache coherency maintenance) requires the
 	 * transfer buffers to live in their own cache lines.
@@ -177,7 +179,7 @@ static ssize_t ad9832_write(struct device *dev, struct device_attribute *attr,
 	if (ret)
 		goto error_ret;
 
-	mutex_lock(&indio_dev->mlock);
+	mutex_lock(&st->lock);
 	switch ((u32)this_attr->address) {
 	case AD9832_FREQ0HM:
 	case AD9832_FREQ1HM:
@@ -238,7 +240,7 @@ static ssize_t ad9832_write(struct device *dev, struct device_attribute *attr,
 	default:
 		ret = -ENODEV;
 	}
-	mutex_unlock(&indio_dev->mlock);
+	mutex_unlock(&st->lock);
 
 error_ret:
 	return ret ? ret : len;
@@ -334,6 +336,7 @@ static int ad9832_probe(struct spi_device *spi)
 
 	st->mclk = pdata->mclk;
 	st->spi = spi;
+	mutex_init(&st->lock);
 
 	indio_dev->dev.parent = &spi->dev;
 	indio_dev->name = spi_get_device_id(spi)->name;