drm/amd/display: Fix use before initialize warning

on stream_for_cursor. Initialize to NULL.
Signed-off-by: Leo (Sunpeng) Li <sunpeng.li@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c

@@ -2124,7 +2124,7 @@ static void dcn10_apply_ctx_for_surface(
 	}
 
 	if (num_planes > 0) {
-		struct dc_stream_state *stream_for_cursor;
+		struct dc_stream_state *stream_for_cursor = NULL;
 
 		program_all_pipe_in_tree(dc, top_pipe_to_program, context);