When removing the old attach function, the racy variable for getting
the last port id became unused.
Fixes: c9cce42876f5 ("ethdev: remove deprecated attach/detach functions")
Cc: stable@dpdk.org
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Reviewed-by: Andrew Rybchenko <arybchenko@solarflare.com>