This retains old behavior for depths <= 24, but allows gamma
table and colormap updates to work properly at depth 30.
This needs the xf86Randr12CrtcComputeGamma() fix for depth 30
from a previous commit to work. Otherwise the server will work,
but gamma table updates will silently fail, iow. the server
would always run with a default identity gamma lut.
v2: Simplify as proposed by Michel.
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Reviewed-by: Antoine Martin <antoine@nagafix.co.uk> (v1)
7bc86c7d23