drm/dp: Staticize a couple of DP utility functions

sparse complains about these functions missing a prototype, but looking
closer they aren't (and likely not supposed to be) used outside of this
source file, so they can be made static.
Signed-off-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -1484,7 +1484,7 @@ static int drm_dp_send_enum_path_resources(struct drm_dp_mst_topology_mgr *mgr,
 	return 0;
 }
 
-int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
+static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
 				   struct drm_dp_mst_port *port,
 				   int id,
 				   int pbn)
@@ -1538,7 +1538,7 @@ static int drm_dp_create_payload_step1(struct drm_dp_mst_topology_mgr *mgr,
 	return 0;
 }
 
-int drm_dp_create_payload_step2(struct drm_dp_mst_topology_mgr *mgr,
+static int drm_dp_create_payload_step2(struct drm_dp_mst_topology_mgr *mgr,
 				       struct drm_dp_mst_port *port,
 				       int id,
 				       struct drm_dp_payload *payload)
@@ -1551,7 +1551,7 @@ int drm_dp_create_payload_step2(struct drm_dp_mst_topology_mgr *mgr,
 	return ret;
 }
 
-int drm_dp_destroy_payload_step1(struct drm_dp_mst_topology_mgr *mgr,
+static int drm_dp_destroy_payload_step1(struct drm_dp_mst_topology_mgr *mgr,
 					struct drm_dp_mst_port *port,
 					int id,
 					struct drm_dp_payload *payload)
@@ -1567,7 +1567,7 @@ int drm_dp_destroy_payload_step1(struct drm_dp_mst_topology_mgr *mgr,
 	return 0;
 }
 
-int drm_dp_destroy_payload_step2(struct drm_dp_mst_topology_mgr *mgr,
+static int drm_dp_destroy_payload_step2(struct drm_dp_mst_topology_mgr *mgr,
 					int id,
 					struct drm_dp_payload *payload)
 {