iio: dac: ad5380: Fix kerneldoc attribute formatting for 'lock'

Kerneldoc expects attributes/parameters to be in '@*.: ' format.

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

 drivers/iio/dac/ad5380.c:64: warning: Function parameter or member 'lock' not described in 'ad5380_state'

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/ad5380.c

@@ -51,7 +51,7 @@ struct ad5380_chip_info {
  * @vref_reg:		vref supply regulator
  * @vref:		actual reference voltage used in uA
  * @pwr_down:		whether the chip is currently in power down mode
- * @lock		lock to protect the data buffer during regmap ops
+ * @lock:		lock to protect the data buffer during regmap ops
  */
 
 struct ad5380_state {