iio: dac: ad5791: Complete 'struct ad5791_chip_info' documentation

... and remove seemingly pointless comment.

Fixes the following W=1 kernel build warning(s):

 drivers/iio/dac/ad5791.c:97: warning: Function parameter or member 'ctrl' not described in 'ad5791_state'
 drivers/iio/dac/ad5791.c:97: warning: Function parameter or member 'pwr_down_mode' not described in 'ad5791_state'
 drivers/iio/dac/ad5791.c:97: warning: Function parameter or member 'pwr_down' not described in 'ad5791_state'
 drivers/iio/dac/ad5791.c:97: warning: Function parameter or member 'data' not described in 'ad5791_state'
 drivers/iio/dac/ad5791.c:103: warning: cannot understand function prototype: 'enum ad5791_supported_device_ids '

Cc: Michael Hennerich <Michael.Hennerich@analog.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/dac/ad5791.c

@@ -76,9 +76,11 @@ struct ad5791_chip_info {
  * @chip_info:		chip model specific constants
  * @vref_mv:		actual reference voltage used
  * @vref_neg_mv:	voltage of the negative supply
- * @pwr_down_mode	current power down mode
+ * @ctrl:		control regster cache
+ * @pwr_down_mode:	current power down mode
+ * @pwr_down:		true if device is powered down
+ * @data:		spi transfer buffers
  */
-
 struct ad5791_state {
 	struct spi_device		*spi;
 	struct regulator		*reg_vdd;
@@ -96,10 +98,6 @@ struct ad5791_state {
 	} data[3] ____cacheline_aligned;
 };
 
-/**
- * ad5791_supported_device_ids:
- */
-
 enum ad5791_supported_device_ids {
 	ID_AD5760,
 	ID_AD5780,