drm/amd/display: Fix missing dc_3dlut forward declaration

[WHY]
The __set_colorop_3dlut() prototype in the KUnit-test section of
amdgpu_dm_color.h references struct dc_3dlut, but no forward
declaration for that struct exists in the header.

The forward declaration was originally present but was repurposed
into struct dc_plane_cm when the adjacent amdgpu_dm_atomic_lut3d()
prototype was updated, leaving __set_colorop_3dlut() without a
declaration for struct dc_3dlut.

[HOW]
Add back forward declaration of struct dc_3dlut alongside the other
forward declarations at the top of the header.

Fixes: b008c67efb36 ("drm/amd/display: Introduce dc_plane_cm and migrate surface update color path")
Cc: Alex Hung <alex.hung@amd.com>
Reviewed-by: Bhawanpreet Lakha <bhawanpreet.lakha@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Wayne Lin <wayne.lin@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

0 files changed, 0 insertions, 0 deletions