webkitgtk: fix compile failure on beaglebone

webkitgtk: fix compile failure on beaglebone

Since the following patch applied in upstream webkitgtk
...
commit 1a55d8c685b3e5b4dbeda202009e7527aa59eadd
Author: simon.fraser@apple.com <simon.fraser@apple.com@268f45cc-cd09-0410-ab3c-d52691b4dbfc>
Date:   Thu Nov 23 22:20:09 2017 +0000

    FELighting cleanup and optimization
    https://bugs.webkit.org/show_bug.cgi?id=179933
...

It missed to tweak `paintingData.lightVector' which caused
PaintingData' has no member named 'lightVector' on ARM_NEON
(beaglebone)

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>