Add dvadym@ to ios/chrome/browser/passwords/OWNERS

Vadym has been fixing bugs in the iOS part of password manager code,
knows it well and should be an owner of it.

Bug: None
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I2623e35a2763cdd85a1c8808b44a1cc23887d22a
Reviewed-on: https://chromium-review.googlesource.com/808266
Commit-Queue: Vadym Doroshenko <dvadym@chromium.org>
Reviewed-by: Vadym Doroshenko <dvadym@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521731}

ios/chrome/browser/passwords/OWNERS

+dvadym@chromium.org
 melandory@chromium.org
 vabr@chromium.org
 vasilii@chromium.org