drm/i915: Remove the pointless 1:1 matrix copy

drm/i915: Remove the pointless 1:1 matrix copy

If we don't have to frob with the user provided ctm matrix there's
no point in copying it over. Just point at the user ctm directly.

Also the matrix gets fully populated by ctm_mult_by_limited() so
no need to zero initialize it.

Cc: Johnson Lin <johnson.lin@intel.com>
Cc: Uma Shankar <uma.shankar@intel.com>
Cc: Shashank Sharma <shashank.sharma@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180222214232.6064-2-ville.syrjala@linux.intel.com
Reviewed-by: Uma Shankar <uma.shankar@intel.com>