[secure storage] Fixes a comment in the OnDiskStorage implementation of secure storage.
[secure storage] Fixes a comment in the OnDiskStorage implementation of secure storage.

Closes: #2580
Approved by: davidiw

libra/libra,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra