drm/i915: Free stolen node on failed preallocation

The odds of this happening are *extremely* unlikely.
Reported-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_stolen.c

@@ -402,7 +402,7 @@ i915_gem_object_create_stolen_for_preallocated(struct drm_device *dev,
 					  &obj->gtt_space);
 		if (ret) {
 			DRM_DEBUG_KMS("failed to allocate stolen GTT space\n");
-			goto unref_out;
+			goto err_out;
 		}
 	}
 
@@ -413,7 +413,8 @@ i915_gem_object_create_stolen_for_preallocated(struct drm_device *dev,
 
 	return obj;
 
-unref_out:
+err_out:
+	drm_mm_put_block(stolen);
 	drm_gem_object_unreference(&obj->base);
 	return NULL;
 }