drm/amd/display: Correct degamma coefficients

[Why]
Some incorrect coefficients were being used

Reviewed-by: Michael Strauss <michael.strauss@amd.com>
Acked-by: Mikita Lipski <mikita.lipski@amd.com>
Signed-off-by: Jaehyun Chung <jaehyun.chung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>