Do not push the CM_GAMMA_LUT property values in drmmode_crtc_cm_init

The crtc->gamma_lut values aren't initialized yet at this point, and
the property values are pushed again from drmmode_setup_colormap
anyway.

Fixes intermittent flicker due to random gamma LUT values during server
startup.

Acked-by: Alex Deucher <alexander.deucher@amd.com>