Fix SnapshotManager instantiation.

New() should be used instead of NewForFirstStageMount().

Bug: 168258606
Test: data wipe with VABC merge in progress
Change-Id: Idf2b01a504b577766da303091721764242e99a69
diff --git a/install/snapshot_utils.cpp b/install/snapshot_utils.cpp
index 7235e67..336e50f 100644
--- a/install/snapshot_utils.cpp
+++ b/install/snapshot_utils.cpp
@@ -32,7 +32,7 @@
   }
 
   RecoveryUI* ui = device->GetUI();
-  auto sm = SnapshotManager::NewForFirstStageMount();
+  auto sm = SnapshotManager::New();
   if (!sm) {
     ui->Print("Could not create SnapshotManager.\n");
     return false;
@@ -57,7 +57,7 @@
     return true;
   }
 
-  auto sm = SnapshotManager::NewForFirstStageMount();
+  auto sm = SnapshotManager::New();
   if (!sm) {
     // SnapshotManager could not be created. The device is still in a
     // consistent state and can continue with the mounting of the existing