[CrOS] Add tellier@google.com to owners of login/lock screen UI

Change-Id: I724335453e7cd4ff4ba51405afbdb4d97802b01d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2529350Reviewed-by: Denis Kuznetsov [CET] <antrim@chromium.org>
Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Commit-Queue: Roman Sorokin [CET] <rsorokin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826208}

ash/login/ui/OWNERS

+# (in CET)
+tellier@google.com
+
 per-file lock_screen.*=set noparent
 per-file lock_screen.*=file://ash/login/LOGIN_LOCK_OWNERS