amdgpu/dm: constify rgb formats.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -3062,7 +3062,7 @@ static const struct drm_plane_helper_funcs dm_plane_helper_funcs = {
  * plane capabilities, or initialize this array to all formats, so internal drm
  * check will succeed, and let DC to implement proper check
  */
-static uint32_t rgb_formats[] = {
+static const uint32_t rgb_formats[] = {
 	DRM_FORMAT_RGB888,
 	DRM_FORMAT_XRGB8888,
 	DRM_FORMAT_ARGB8888,