drm/amd/display: Fix null check of pipe_ctx->plane_state for update_dchubp_dpp

Similar to commit 6a05707 ("drm/amd/display: Fix null check for
pipe_ctx->plane_state in dcn20_program_pipe") that addresses a null
pointer dereference on dcn20_update_dchubp_dpp. This is the same
function hooked for update_dchubp_dpp in dcn401, with the same issue.
Fix possible null pointer deference on dcn401_program_pipe too.

Fixes: 63ab80d ("drm/amd/display: DML2.1 Post-Si Cleanup")
Signed-off-by: Melissa Wen <mwen@igalia.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit d8d47f7)

Author: melissawen

drivers/gpu/drm/amd/display/dc/hwss/dcn401/dcn401_hwseq.c

@@ -1980,9 +1980,9 @@ void dcn401_program_pipe(
 				dc->res_pool->hubbub, pipe_ctx->plane_res.hubp->inst, pipe_ctx->hubp_regs.det_size);
 	}
 
-	if (pipe_ctx->update_flags.raw ||
-		(pipe_ctx->plane_state && pipe_ctx->plane_state->update_flags.raw) ||
-		pipe_ctx->stream->update_flags.raw)
+	if (pipe_ctx->plane_state && (pipe_ctx->update_flags.raw ||
+	    pipe_ctx->plane_state->update_flags.raw ||
+	    pipe_ctx->stream->update_flags.raw))
 		dc->hwss.update_dchubp_dpp(dc, pipe_ctx, context);
 
 	if (pipe_ctx->plane_state && (pipe_ctx->update_flags.bits.enable ||