libevdev: update ebuild slot number for upcoming rename

Other ebuild files now depend using :=

BUG=b:191824146
TEST=manual testing

Change-Id: I9cdae4022088cd1a46b5d33f4cfb5b43009b556b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/2987320
Tested-by: Nicholas Verne <nverne@chromium.org>
Reviewed-by: Fergus Dall <sidereal@google.com>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
4 files changed