drm/amd/display: fix virtual signal dsc setup

This prevents dpcd access on virtual links.
Signed-off-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Reviewed-by: Eric Bernstein <Eric.Bernstein@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -400,7 +400,7 @@ static bool dp_set_dsc_on_rx(struct pipe_ctx *pipe_ctx, bool enable)
 	struct dc_stream_state *stream = pipe_ctx->stream;
 	bool result = false;
 
-	if (IS_FPGA_MAXIMUS_DC(dc->ctx->dce_environment))
+	if (dc_is_virtual_signal(stream->signal) || IS_FPGA_MAXIMUS_DC(dc->ctx->dce_environment))
 		result = true;
 	else
 		result = dm_helpers_dp_write_dsc_enable(dc->ctx, stream, enable);