iio: trigger: Add missing fields in kernel docs

Fix kernel docs warnings by adding the missing description
for each of the existing function parameters.

Signed-off-by: Cristina Opriceana <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/industrialio-trigger.c

···
 
 /**
  * iio_trigger_read_name() - retrieve useful identifying name
- **/
+ * @dev:	device associated with the iio_trigger
+ * @attr:	pointer to the device_attribute structure that is
+ *		being processed
+ * @buf:	buffer to print the name into
+ *
+ * Return: a negative number on failure or the number of written
+ *	   characters on success.
+ */
 static ssize_t iio_trigger_read_name(struct device *dev,
 				     struct device_attribute *attr,
 				     char *buf)
···
 
 /**
  * iio_trigger_read_current() - trigger consumer sysfs query current trigger
+ * @dev:	device associated with an industrial I/O device
+ * @attr:	pointer to the device_attribute structure that
+ *		is being processed
+ * @buf:	buffer where the current trigger name will be printed into
  *
  * For trigger consumers the current_trigger interface allows the trigger
  * used by the device to be queried.
- **/
+ *
+ * Return: a negative number on failure, the number of characters written
+ *	   on success or 0 if no trigger is available
+ */
 static ssize_t iio_trigger_read_current(struct device *dev,
 					struct device_attribute *attr,
 					char *buf)
···
 
 /**
  * iio_trigger_write_current() - trigger consumer sysfs set current trigger
+ * @dev:	device associated with an industrial I/O device
+ * @attr:	device attribute that is being processed
+ * @buf:	string buffer that holds the name of the trigger
+ * @len:	length of the trigger name held by buf
  *
  * For trigger consumers the current_trigger interface allows the trigger
  * used for this device to be specified at run time based on the trigger's
  * name.
- **/
+ *
+ * Return: negative error code on failure or length of the buffer
+ *	   on success
+ */
 static ssize_t iio_trigger_write_current(struct device *dev,
 					 struct device_attribute *attr,
 					 const char *buf,