drm/i915: Move the gtt mm takedown to cleanup

Our VM code already has a cleanup function, and this is a nice place to
put the drm_mm_takedown. This should have no functional impact, it just
leaves the unload function a bit cleaer, and is more logical IMO

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index c1d04a3..056f1f0 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -1411,6 +1411,8 @@
 {
 
 	struct i915_gtt *gtt = container_of(vm, struct i915_gtt, base);
+
+	drm_mm_takedown(&vm->mm);
 	iounmap(gtt->gsm);
 	teardown_scratch_page(vm->dev);
 }