soundwire: add missing kernel-doc description

For some reason we never added a description for the clk_stop
callback.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
Reviewed-by: Rander Wang <rander.wang@intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Link: https://lore.kernel.org/r/20210511030048.25622-3-yung-chuan.liao@linux.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

include/linux/soundwire/sdw.h

@@ -612,6 +612,7 @@ struct sdw_bus_params {
  * @update_status: Update Slave status
  * @bus_config: Update the bus config for Slave
  * @port_prep: Prepare the port with parameters
+ * @clk_stop: handle imp-def sequences before and after prepare and de-prepare
  */
 struct sdw_slave_ops {
 	int (*read_prop)(struct sdw_slave *sdw);