drm/i915: s/blob_data/lut/

We're talking about LUT contents here so let's call the thing
'lut' rather than 'blob_data'. This is the name the load_lut()
code used before already.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200303173313.28117-5-ville.syrjala@linux.intel.com
Reviewed-by: Swati Sharma <swati2.sharma@intel.com>