drm/i915: Use LINEAR modifier instead of NONE

They're the same, so use the one which makes more sense.

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Link: http://patchwork.freedesktop.org/patch/msgid/20170324212950.2206-1-ben@bwidawsk.net


Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>