libscrypt: add OWNERS

This CL adds owners for libscrypt package.

BUG=none
TEST=none

Change-Id: I4ac93321b4156a5c53f5270726a3d19130e03347
Reviewed-on: https://chromium-review.googlesource.com/1654329
Tested-by: Andrey Pronin <apronin@chromium.org>
Commit-Ready: Andrey Pronin <apronin@chromium.org>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Andrey Pronin <apronin@chromium.org>