iio: dac: ad5446: Complete 'struct ad5446_state' doc and demote unworthy kerneldocs

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

 drivers/iio/dac/ad5446.c:48: warning: Function parameter or member 'dev' not described in 'ad5446_state'
 drivers/iio/dac/ad5446.c:48: warning: Function parameter or member 'cached_val' not described in 'ad5446_state'
 drivers/iio/dac/ad5446.c:48: warning: Function parameter or member 'pwr_down_mode' not described in 'ad5446_state'
 drivers/iio/dac/ad5446.c:48: warning: Function parameter or member 'pwr_down' not described in 'ad5446_state'
 drivers/iio/dac/ad5446.c:48: warning: Function parameter or member 'lock' not described in 'ad5446_state'
 drivers/iio/dac/ad5446.c:323: warning: cannot understand function prototype: 'enum ad5446_supported_spi_device_ids '
 drivers/iio/dac/ad5446.c:545: warning: cannot understand function prototype: 'enum ad5446_supported_i2c_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/ad5446.c

@@ -29,11 +29,14 @@
 
 /**
  * struct ad5446_state - driver instance specific data
- * @spi:		spi_device
+ * @dev:		this device
  * @chip_info:		chip model specific constants, available modes etc
  * @reg:		supply regulator
  * @vref_mv:		actual reference voltage used
- * @lock		lock to protect the data buffer during write ops
+ * @cached_val:		store/retrieve values during power down
+ * @pwr_down_mode:	power down mode (1k, 100k or tristate)
+ * @pwr_down:		true if the device is in power down
+ * @lock:		lock to protect the data buffer during write ops
  */
 
 struct ad5446_state {
@@ -311,7 +314,7 @@ static int ad5660_write(struct ad5446_state *st, unsigned val)
 	return spi_write(spi, data, sizeof(data));
 }
 
-/**
+/*
  * ad5446_supported_spi_device_ids:
  * The AD5620/40/60 parts are available in different fixed internal reference
  * voltage options. The actual part numbers may look differently
@@ -533,7 +536,7 @@ static int ad5622_write(struct ad5446_state *st, unsigned val)
 	return i2c_master_send(client, (char *)&data, sizeof(data));
 }
 
-/**
+/*
  * ad5446_supported_i2c_device_ids:
  * The AD5620/40/60 parts are available in different fixed internal reference
  * voltage options. The actual part numbers may look differently