drm/dp: Add missing kernel-doc

Commit 9dc40560 (drm/dp: let drivers specify the name of the I2C-
over-AUX adapter) introduced a new field but didn't add the proper
kernel-doc for it.
Signed-off-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

include/drm/drm_dp_helper.h

@@ -509,6 +509,7 @@ struct drm_dp_aux_msg {
 
 /**
  * struct drm_dp_aux - DisplayPort AUX channel
+ * @name: user-visible name of this AUX channel and the I2C-over-AUX adapter
  * @ddc: I2C adapter that can be used for I2C-over-AUX communication
  * @dev: pointer to struct device that is the parent for this AUX channel
  * @transfer: transfers a message representing a single AUX transaction