drm/msm/gem: Drop early returns in close/purge vma

Keep the warn, but drop the early return.  If we do manage to hit this
sort of issue, skipping the cleanup just makes things worse (dangling
drm_mm_nodes when the msm_gem_vma is freed, etc).  Whereas the worst
that happens if we tear down a mapping the GPU is accessing is that we
get GPU iova faults, but otherwise the world keeps spinning.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Tested-by: Steev Klimaszewski <steev@kali.org>
Reported-by: Steev Klimaszewski <steev@kali.org>
Patchwork: https://patchwork.freedesktop.org/patch/489115/
Link: https://lore.kernel.org/r/20220610172055.2337977-1-robdclark@gmail.com