fs_mgr: support -o sync

Bug: 134172577
Change-Id: I1ad8811b07657727d8227d3668f58b0fbc7e7609
Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>
diff --git a/fs_mgr/fs_mgr_fstab.cpp b/fs_mgr/fs_mgr_fstab.cpp
index b6c65da..403f9be 100644
--- a/fs_mgr/fs_mgr_fstab.cpp
+++ b/fs_mgr/fs_mgr_fstab.cpp
@@ -61,6 +61,7 @@
         {"nodiratime", MS_NODIRATIME},
         {"ro", MS_RDONLY},
         {"rw", 0},
+        {"sync", MS_SYNCHRONOUS},
         {"remount", MS_REMOUNT},
         {"bind", MS_BIND},
         {"rec", MS_REC},