drm/amd/display: Constify dcn20_res_pool_funcs

The only usage of dcn20_res_pool_funcs is to assign its address to a
const pointer. Make it const to allow the compiler to put it in
read-only memory.
Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c

@@ -3320,7 +3320,7 @@ enum dc_status dcn20_patch_unknown_plane_state(struct dc_plane_state *plane_stat
 	return DC_OK;
 }
 
-static struct resource_funcs dcn20_res_pool_funcs = {
+static const struct resource_funcs dcn20_res_pool_funcs = {
 	.destroy = dcn20_destroy_resource_pool,
 	.link_enc_create = dcn20_link_encoder_create,
 	.panel_cntl_create = dcn20_panel_cntl_create,