st/nine: Fix leak with volume dtor

The last level was not released.

Signed-off-by: Axel Davy <axel.davy@ens.fr>
diff --git a/src/gallium/state_trackers/nine/volumetexture9.c b/src/gallium/state_trackers/nine/volumetexture9.c
index 4908ed7..5c83fdb 100644
--- a/src/gallium/state_trackers/nine/volumetexture9.c
+++ b/src/gallium/state_trackers/nine/volumetexture9.c
@@ -139,7 +139,7 @@
     DBG("This=%p\n", This);
 
     if (This->volumes) {
-        for (l = 0; l < This->base.base.info.last_level; ++l)
+        for (l = 0; l <= This->base.base.info.last_level; ++l)
             NineUnknown_Destroy(&This->volumes[l]->base);
         FREE(This->volumes);
     }