drm/i915/gtt: Remove superfluous free_pd with gen6/7

This has slipped in somewhere but it was harmless
as we check the page pointer before teardown.
Signed-off-by: NMika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: NMichel Thierry <michel.thierry@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -1379,7 +1379,6 @@ static void gen6_ppgtt_cleanup(struct i915_address_space *vm)
 	}
 
 	free_pt(ppgtt->base.dev, ppgtt->scratch_pt);
-	free_pd(ppgtt->base.dev, &ppgtt->pd);
 }
 
 static int gen6_ppgtt_allocate_page_directories(struct i915_hw_ppgtt *ppgtt)