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 <[email protected]>
Reviewed-by: Lyude Paul <[email protected]>
Acked-by: Alex Deucher <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: Hans Verkuil

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;