drm/amd/display: Ignore Transitional Invalid Link Rate Error Message

[Why]
When hotplug or unplug happens, each stream disabled one by one, and then
enable any alived streams. Link phy and payload table is cleared when 1st
stream is disabled. That causes the error message pops up when disable 2nd
stream. There is no active stream after link_rate is cleared.
After all streams are disabled, link will be trained again and link rate is
assigned to any alived streams.

Therefore there is no harm for the error message that represents invalid
link rate value in the atomic reset transitional time period.

[How]
Downgrade the log level from ERROR to DEBUG.
Reviewed-by: Wayne Lin <Wayne.Lin@amd.com>
Acked-by: Solomon Chiu <solomon.chiu@amd.com>
Signed-off-by: Fangzhi Zuo <Jerry.Zuo@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc_link.c

@@ -3928,7 +3928,7 @@ static enum dc_status deallocate_mst_payload(struct pipe_ctx *pipe_ctx)
 				&link->mst_stream_alloc_table);
 		break;
 	case DP_UNKNOWN_ENCODING:
-		DC_LOG_ERROR("Failure: unknown encoding format\n");
+		DC_LOG_DEBUG("Unknown encoding format\n");
 		return DC_ERROR_UNEXPECTED;
 	}