[chromecast] Add bcf@ to chromecast/device/bluetooth OWNERS

So I we can stop bothering slan@ with these CLs :)

Bug: None
Test: None
Change-Id: I855507f13d41d6e611ce00a421862f28f380324e
Reviewed-on: https://chromium-review.googlesource.com/1153781Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Commit-Queue: Bailey Forrest <bcf@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579132}

chromecast/device/bluetooth/OWNERS

+bcf@chromium.org
 slan@chromium.org