overview: Add sammiequon@ to OWNERS.

Test: none
Bug: none
Change-Id: Idf8dc27a75ccbf3040e0f5950565d1dc856cc9a8
Reviewed-on: https://chromium-review.googlesource.com/c/1306664Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604000}

ash/wm/overview/OWNERS

+sammiequon@chromium.org
 xdai@chromium.org
 
 # COMPONENT: UI>Shell>OverviewMode