drm/dp: fix kernel-doc warnings at drm_dp_helper.c

As warned by kernel-doc:

	./drivers/gpu/drm/drm_dp_helper.c:385: warning: Function parameter or member 'type' not described in 'drm_dp_downstream_is_type'
	./drivers/gpu/drm/drm_dp_helper.c:886: warning: Function parameter or member 'dev' not described in 'drm_dp_downstream_mode'

Some function parameters weren't documented.

Fixes: 38784f6f ("drm/dp: Add helpers to identify downstream facing port types")
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/03c9c8ba3f492aca76e2b4836803219cd9c971cf.1603791716.git.mchehab+huawei@kernel.org

drivers/gpu/drm/drm_dp_helper.c

@@ -374,6 +374,10 @@ static bool is_edid_digital_input_dp(const struct edid *edid)
  * drm_dp_downstream_is_type() - is the downstream facing port of certain type?
  * @dpcd: DisplayPort configuration data
  * @port_cap: port capabilities
+ * @type: port type to be checked. Can be:
+ * 	  %DP_DS_PORT_TYPE_DP, %DP_DS_PORT_TYPE_VGA, %DP_DS_PORT_TYPE_DVI,
+ * 	  %DP_DS_PORT_TYPE_HDMI, %DP_DS_PORT_TYPE_NON_EDID,
+ *	  %DP_DS_PORT_TYPE_DP_DUALMODE or %DP_DS_PORT_TYPE_WIRELESS.
  *
  * Caveat: Only works with DPCD 1.1+ port caps.
  *
@@ -870,6 +874,7 @@ EXPORT_SYMBOL(drm_dp_downstream_444_to_420_conversion);
 
 /**
  * drm_dp_downstream_mode() - return a mode for downstream facing port
+ * @dev: DRM device
  * @dpcd: DisplayPort configuration data
  * @port_cap: port capabilities
  *