drm/amd/display: Fix dim display on DCE11

Before programming the input gamma, check that we're not using the
identity correction.

Signed-off-by: Leo (Sunpeng) Li <sunpeng.li@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@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/dce110/dce110_hw_sequencer.c

@@ -280,7 +280,9 @@ dce110_set_input_transfer_func(struct pipe_ctx *pipe_ctx,
 	build_prescale_params(&prescale_params, plane_state);
 	ipp->funcs->ipp_program_prescale(ipp, &prescale_params);
 
-	if (plane_state->gamma_correction && dce_use_lut(plane_state->format))
+	if (plane_state->gamma_correction &&
+			!plane_state->gamma_correction->is_identity &&
+			dce_use_lut(plane_state->format))
 		ipp->funcs->ipp_program_input_lut(ipp, plane_state->gamma_correction);
 
 	if (tf == NULL) {