[Autofill Assistant] Add Mathias and I as owners

Change-Id: I71ed01f39d1c81c62828d8e4900091e7941e7ab1
Reviewed-on: https://chromium-review.googlesource.com/c/1278399Reviewed-by: Ganggui Tang <gogerald@chromium.org>
Commit-Queue: Ganggui Tang <gogerald@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599194}

components/autofill_assistant/OWNERS

 gogerald@chromium.org
+mcarlen@chromium.org
 rouslan@chromium.org
+szermatt@chromium.org
 
 # COMPONENT: UI>Browser>Autofill