drm/amd/display: Null check for gamma correction.

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/dcn10/dcn10_hw_sequencer.c

@@ -900,7 +900,8 @@ static bool dcn10_set_input_transfer_func(struct pipe_ctx *pipe_ctx,
 	if (plane_state->in_transfer_func)
 		tf = plane_state->in_transfer_func;
 
-	if (plane_state->gamma_correction->is_identity)
+	if (plane_state->gamma_correction &&
+		plane_state->gamma_correction->is_identity)
 		dpp_base->funcs->dpp_set_degamma(dpp_base, IPP_DEGAMMA_MODE_BYPASS);
 	else if (plane_state->gamma_correction && dce_use_lut(plane_state->format))
 		dpp_base->funcs->dpp_program_input_lut(dpp_base, plane_state->gamma_correction);