iio: adc: ltc2947-core: 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]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/adc/ltc2497-core.c

···
 #include <linux/iio/iio.h>
 #include <linux/iio/driver.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/regulator/consumer.h>
 
 #include "ltc2497.h"
···
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
-		mutex_lock(&indio_dev->mlock);
+		mutex_lock(&ddata->lock);
 		ret = ltc2497core_read(ddata, chan->address, val);
-		mutex_unlock(&indio_dev->mlock);
+		mutex_unlock(&ddata->lock);
 		if (ret < 0)
 			return ret;
 
···
 
 	ddata->addr_prev = LTC2497_CONFIG_DEFAULT;
 	ddata->time_prev = ktime_get();
+
+	mutex_init(&ddata->lock);
 
 	ret = iio_device_register(indio_dev);
 	if (ret < 0)

drivers/iio/adc/ltc2497.h

···
 struct ltc2497core_driverdata {
 	struct regulator *ref;
 	ktime_t	time_prev;
+	/* lock to protect against multiple access to the device */
+	struct mutex lock;
 	const struct ltc2497_chip_info	*chip_info;
 	u8 addr_prev;
 	int (*result_and_measure)(struct ltc2497core_driverdata *ddata,