drm/i915: Only do gtt cleanup in vma_unbind for the global vma

Otherwise we end up tearing down fences when e.g. the client quits
way too early. Might or might not fix a fence pin_count BUG Ville has
reported.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -2761,12 +2761,14 @@ int i915_vma_unbind(struct i915_vma *vma)
 	 * cause memory corruption through use-after-free.
 	 */
 
-	i915_gem_object_finish_gtt(obj);
+	if (i915_is_ggtt(vma->vm)) {
+		i915_gem_object_finish_gtt(obj);
 
-	/* release the fence reg _after_ flushing */
-	ret = i915_gem_object_put_fence(obj);
-	if (ret)
-		return ret;
+		/* release the fence reg _after_ flushing */
+		ret = i915_gem_object_put_fence(obj);
+		if (ret)
+			return ret;
+	}
 
 	trace_i915_vma_unbind(vma);