staging:iio:ad7606: update structs with doc annotations

The current structs are only partially documented via annotations. This
change updates annotations for all structs in the ad7606.h file.
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/adc/ad7606.h

@@ -22,7 +22,27 @@ struct ad7606_chip_info {
 
 /**
  * struct ad7606_state - driver instance specific data
- * @lock		protect sensor state
+ * @dev		pointer to kernel device
+ * @chip_info		entry in the table of chips that describes this device
+ * @reg		regulator info for the the power supply of the device
+ * @poll_work		work struct for continuously reading data from the device
+ *			into an IIO triggered buffer
+ * @wq_data_avail	wait queue struct for buffer mode
+ * @bops		bus operations (SPI or parallel)
+ * @range		voltage range selection, selects which scale to apply
+ * @oversampling	oversampling selection
+ * @done		marks whether reading data is done
+ * @base_address	address from where to read data in parallel operation
+ * @lock		protect sensor state from concurrent accesses to GPIOs
+ * @gpio_convst	GPIO descriptor for conversion start signal (CONVST)
+ * @gpio_reset		GPIO descriptor for device hard-reset
+ * @gpio_range		GPIO descriptor for range selection
+ * @gpio_standby	GPIO descriptor for stand-by signal (STBY),
+ *			controls power-down mode of device
+ * @gpio_frstdata	GPIO descriptor for reading from device when data
+ *			is being read on the first channel
+ * @gpio_os		GPIO descriptors to control oversampling on the device
+ * @data		buffer for reading data from the device
  */
 
 struct ad7606_state {
@@ -53,6 +73,10 @@ struct ad7606_state {
 	unsigned short			data[12] ____cacheline_aligned;
 };
 
+/**
+ * struct ad7606_bus_ops - driver bus operations
+ * @read_block		function pointer for reading blocks of data
+ */
 struct ad7606_bus_ops {
 	/* more methods added in future? */
 	int (*read_block)(struct device *dev, int num, void *data);