WRITE_ONCE() should happen at the original var, not on a local
copy of it.

Cc: stable@vger.kernel.org
Fixes: 5d36acb7 ("drm/i915/gt: Batch TLB invalidations")
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
[added cc-stable while merging it]
Link: https://patchwork.freedesktop.org/patch/msgid/f9550e6bacea10131ff40dd8981b69eb9251cdcd.1659598090.git.mchehab@kernel.org