drm_dp_mst_topology: fix broken drm_dp_sideband_parse_remote_dpcd_read()

When parsing the reply of a DP_REMOTE_DPCD_READ DPCD command the
result is wrong due to a missing idx increment.

This was never noticed since DP_REMOTE_DPCD_READ is currently not
used, but if you enable it, then it is all wrong.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/e72ddac2-1dc0-100a-d816-9ac98ac009dd@xs4all.nl

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -439,6 +439,7 @@ static bool drm_dp_sideband_parse_remote_dpcd_read(struct drm_dp_sideband_msg_rx
 	if (idx > raw->curlen)
 		goto fail_len;
 	repmsg->u.remote_dpcd_read_ack.num_bytes = raw->msg[idx];
+	idx++;
 	if (idx > raw->curlen)
 		goto fail_len;