os: fix findOneDriveDir to expand REG_SZ registry values
On some Windows systems the SOFTWARE\Microsoft\OneDrive registry key is REG_SZ rather than REG_EXPAND_SZ.
Change-Id: I3ccb8771377a73456f48da1b5cfae668130b3f7b
Reviewed-on: https://go-review.googlesource.com/c/go/+/623515 Reviewed-by: Quim Muntal <quimmuntal@gmail.com> Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com> Reviewed-by: Carlos Amedee <carlos@golang.org>