remount: Remove the "backing" parameter to fs_mgr_overlayfs_setup.

This is unused.

Bug: 241179247
Test: remount
Change-Id: I7a9e07a4cf397c6fc8909a9959e08d1aefa3216a
diff --git a/set-verity-state/set-verity-state.cpp b/set-verity-state/set-verity-state.cpp
index d8e3d31..ac91ca0 100644
--- a/set-verity-state/set-verity-state.cpp
+++ b/set-verity-state/set-verity-state.cpp
@@ -52,7 +52,7 @@
   auto change = false;
   errno = 0;
   if (enable ? fs_mgr_overlayfs_teardown(nullptr, &change)
-             : fs_mgr_overlayfs_setup(nullptr, nullptr, &change)) {
+             : fs_mgr_overlayfs_setup(nullptr, &change)) {
     if (change) {
       printf("%s overlayfs\n", enable ? "disabling" : "using");
     }