drm/i915: Fix race in __i915_vma_remove_closed

i915_vma_reopen checked if the vma is closed before without taking the
lock. So multiple threads could attempt removing the vma.

Instead the lock needs to be taken before actually checking.

v2: move struct declaration

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: intel-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v5.3+
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5732


Signed-off-by: Karol Herbst <kherbst@redhat.com>
Fixes: 155ab883 ("drm/i915: Move object close under its own lock")
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220420095720.3331609-1-kherbst@redhat.com