rmi4update: Add readlinkat to seccomp policies

Fixes a crash noticed in builders:
exe="/usr/sbin/rmi4update" sig=31 SYSCALL=readlinkat

BUG=b:235960683
TEST=CQ

Change-Id: Ie05a5c7d0b570570d806949cc292a51b1b69d4de
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/touch_updater/+/3916357
Tested-by: Manoj Gupta <manojgupta@chromium.org>
Auto-Submit: Manoj Gupta <manojgupta@chromium.org>
Reviewed-by: Sean O'Brien <seobrien@chromium.org>
4 files changed