drm/amd/display: Fix shaper using bad LUT params

[Why]
LUT params are not cleared after setting blend TF, which can lead to
same params being used for the shaper, if the shaper func is bypassed.

[How]
Set lut_params to NULL after program_1dlut.

Reviewed-by: Krunoslav Kovac <krunoslav.kovac@amd.com>
Acked-by: Roman Li <roman.li@amd.com>
Signed-off-by: Ilya Bakoulin <ilya.bakoulin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>