drm/amd/display: don't crash if stream is NULL when trying to share clocks

Signed-off-by: Yongqiang Sun <yongqiang.sun@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -288,6 +288,11 @@ static bool is_sharable_clk_src(
 	if (pipe_with_clk_src->clock_source == NULL)
 		return false;
 
+	if (pipe_with_clk_src->stream == NULL) {
+		ASSERT(0);
+		return false;
+	}
+
 	if (pipe_with_clk_src->stream->signal == SIGNAL_TYPE_VIRTUAL)
 		return false;