Fix cleanup order of SW stats structures to be reversed
to initialization order.
Fixes: fdd7719eb3 ("net/sfc: add xstats for Rx/Tx doorbells")
Cc: stable@dpdk.org
Signed-off-by: Ivan Ilchenko <ivan.ilchenko@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>