drm/ttm: Fix TTM object open regression

Commit drm/ttm: ttm object security fixes for render nodes introduced a
regression where, if a TTM object was opened multiple times from the same
open file, the caller would spin uninterruptibly in the kernel.

Fix this.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jakob Bornecrantz <jakob@vmware.com>

drivers/gpu/drm/ttm/ttm_object.c

@@ -292,7 +292,7 @@ int ttm_ref_object_add(struct ttm_object_file *tfile,
 
 		if (ret == 0) {
 			ref = drm_hash_entry(hash, struct ttm_ref_object, hash);
-			if (!kref_get_unless_zero(&ref->kref)) {
+			if (kref_get_unless_zero(&ref->kref)) {
 				rcu_read_unlock();
 				break;
 			}