Confirm a11y shortcut service for correct user

Fix came from Sony:
https://partner-android-review.googlesource.com/#/c/829546/

Bug: 62251151
Test: Change shortcut to Switch Access for main user, then
create guest and activate shortcut. The UI used to display
switch access for the guest user as well. Now it displays
TalkBack (which is the service that gets activated by the
shortcut for the Guest; only the UI was wrong.)

Change-Id: If2b90cf260279a342c0ccfde0600544490788d38