anv: Fill holes in the VF VUE to zero

This fixes a GPU hang in DOOM 2016 running under wine.

Cc: mesa-stable@lists.freedesktop.org
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104809


Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
(cherry picked from commit 76b0e4d8)