apparmor: fix change_hat not finding hat after policy replacement

After a policy replacement, the task cred may be out of date and need
to be updated. However change_hat is using the stale profiles from
the out of date cred resulting in either: a stale profile being applied
or, incorrect failure when searching for a hat profile as it has been
migrated to the new parent profile.

Fixes: 01e2b670 (failure to find hat)
Fixes: 898127c3 (stale policy being applied)
Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=1000287


Cc: stable@vger.kernel.org
Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>