drm/i915/fbc: __intel_fbc_cleanup_cfb() may be called multiple times

Avoid releasing the same stolen nodes causing a use-after-free and/or
explosions as the self-checks fail, as __intel_fbc_cleanup_cfb() may be
called multiple times during module unload.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200130135136.1878646-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/display/intel_fbc.c

@@ -537,13 +537,15 @@ static void __intel_fbc_cleanup_cfb(struct drm_i915_private *dev_priv)
 {
 	struct intel_fbc *fbc = &dev_priv->fbc;
 
-	if (drm_mm_node_allocated(&fbc->compressed_fb))
-		i915_gem_stolen_remove_node(dev_priv, &fbc->compressed_fb);
+	if (!drm_mm_node_allocated(&fbc->compressed_fb))
+		return;
 
 	if (fbc->compressed_llb) {
 		i915_gem_stolen_remove_node(dev_priv, fbc->compressed_llb);
 		kfree(fbc->compressed_llb);
 	}
+
+	i915_gem_stolen_remove_node(dev_priv, &fbc->compressed_fb);
 }
 
 void intel_fbc_cleanup_cfb(struct drm_i915_private *dev_priv)