drm/i915: Setup less PPGTT on failed page_directory

The current code will both potentially print a WARN, and setup part of
the PPGTT structure. Neither of these harm the current code, it is
simply for clarity, and to perhaps prevent later bugs, or weird
debug messages.
Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
Signed-off-by: NMichel Thierry <michel.thierry@intel.com>
Reviewed-by: NMika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -1032,11 +1032,14 @@ static int gen6_ppgtt_allocate_page_directories(struct i915_hw_ppgtt *ppgtt)
 		goto alloc;
 	}
 
+	if (ret)
+		return ret;
+
 	if (ppgtt->node.start < dev_priv->gtt.mappable_end)
 		DRM_DEBUG("Forced to use aperture for PDEs\n");
 
 	ppgtt->num_pd_entries = GEN6_PPGTT_PD_ENTRIES;
-	return ret;
+	return 0;
 }
 
 static int gen6_ppgtt_allocate_page_tables(struct i915_hw_ppgtt *ppgtt)