radeon: completely remove lut leftovers

This is an oversight from

commit 42585395


Author: Peter Rosin <peda@axentia.se>
Date:   Thu Jul 13 18:25:36 2017 +0200

    drm: radeon: remove dead code and pointless local lut storage

v2: Also remove leftover local variable.

Cc: Peter Rosin <peda@axentia.se>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>