[Omnibox] Fix smaller margin variant's mv padding

Bug: 1445688
Change-Id: Icd464a85f131f66c3cee5ca098a168fcacc5b19e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4544880


Reviewed-by: Tomasz Wiszkowski <ender@google.com>
Commit-Queue: Patrick Noland <pnoland@chromium.org>
Code-Coverage: Findit <findit-for-me@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1146718}