iio: adc: imx7d_adc: do not use internal iio_dev lock

The iio_device lock is only meant for internal use. Hence define a
device local lock to protect against concurrent accesses.

While at it, properly include "mutex.h" for mutex related APIs.

Signed-off-by: Nuno Sá <[e-mail]>
Reviewed-by: Haibo Chen <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/adc/imx7d_adc.c

···
 #include <linux/kernel.h>
 #include <linux/mod_devicetable.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/platform_device.h>
 #include <linux/regulator/consumer.h>
 
···
 	struct device *dev;
 	void __iomem *regs;
 	struct clk *clk;
-
+	/* lock to protect against multiple access to the device */
+	struct mutex lock;
 	u32 vref_uv;
 	u32 value;
 	u32 channel;
···
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
-		mutex_lock(&indio_dev->mlock);
+		mutex_lock(&info->lock);
 		reinit_completion(&info->completion);
 
 		channel = chan->channel & 0x03;
···
 		ret = wait_for_completion_interruptible_timeout
 				(&info->completion, IMX7D_ADC_TIMEOUT);
 		if (ret == 0) {
-			mutex_unlock(&indio_dev->mlock);
+			mutex_unlock(&info->lock);
 			return -ETIMEDOUT;
 		}
 		if (ret < 0) {
-			mutex_unlock(&indio_dev->mlock);
+			mutex_unlock(&info->lock);
 			return ret;
 		}
 
 		*val = info->value;
-		mutex_unlock(&indio_dev->mlock);
+		mutex_unlock(&info->lock);
 		return IIO_VAL_INT;
 
 	case IIO_CHAN_INFO_SCALE:
···
 	ret = devm_add_action_or_reset(dev, __imx7d_adc_disable, dev);
 	if (ret)
 		return ret;
+
+	mutex_init(&info->lock);
 
 	ret = devm_iio_device_register(dev, indio_dev);
 	if (ret) {