iio: dac: ad5449: 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/ad5449.c:75: warning: Function parameter or member 'lock' not described in 'ad5449'

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/ad5449.c

@@ -56,7 +56,7 @@ struct ad5449_chip_info {
  * @has_sdo:		whether the SDO line is connected
  * @dac_cache:		Cache for the DAC values
  * @data:		spi transfer buffers
- * @lock		lock to protect the data buffer during SPI ops
+ * @lock:		lock to protect the data buffer during SPI ops
  */
 struct ad5449 {
 	struct spi_device		*spi;