drm/nouveau: don't munge in drm_mm internals

Nouveau was checking drm_mm internals on teardown to see whether the
memory manager was initialized. Hide these internals in a small
inline helper function.

Acked-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/include/drm/drm_mm.h b/include/drm/drm_mm.h
index e391777..0d79146 100644
--- a/include/drm/drm_mm.h
+++ b/include/drm/drm_mm.h
@@ -72,6 +72,11 @@
 	unsigned long scan_end;
 };
 
+static inline bool drm_mm_initialized(struct drm_mm *mm)
+{
+	return mm->free_stack.next;
+}
+
 /*
  * Basic range manager support (drm_mm.c)
  */