drm/nouveau: zero vma pointer even if we only unreference it rather than free

I'm not sure this affects anything, but best be safe.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
This commit is contained in:
Ben Skeggs 2020-01-23 13:55:19 +10:00
commit 4c9ee1bfca