Revert "drm/dp_mst: Retrieve extended DPCD caps for topology manager"

This reverts commit ad44c032.

Currently DRM driver assume the source device caps is higher than the MST device
caps. With this commit, this statement would be broken.

e.g. the source device only support DP1.2 and the mst device support DP1.4.
Signed-off-by: Koba Ko <koba.ko@canonical.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201103034907.72129-1-koba.ko@canonical.com

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -3686,10 +3686,9 @@ int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool ms
 		WARN_ON(mgr->mst_primary);
 
 		/* get dpcd info */
-		ret = drm_dp_read_dpcd_caps(mgr->aux, mgr->dpcd);
-		if (ret < 0) {
-			drm_dbg_kms(mgr->dev, "%s: failed to read DPCD, ret %d\n",
-				    mgr->aux->name, ret);
+		ret = drm_dp_dpcd_read(mgr->aux, DP_DPCD_REV, mgr->dpcd, DP_RECEIVER_CAP_SIZE);
+		if (ret != DP_RECEIVER_CAP_SIZE) {
+			DRM_DEBUG_KMS("failed to read DPCD\n");
 			goto out_unlock;
 		}