net: sparx5: Fix get_stat64 crash in tcpdump

This problem was found with Sparx5 when the tcpdump tool requests the
do_get_stats64 (sparx5_get_stats64) statistic.

The portstats pointer was incorrectly incremented when fetching priority
based statistics.

Fixes: af4b1102

 (net: sparx5: add ethtool configuration and statistics support)
Signed-off-by: Steen Hegelund <steen.hegelund@microchip.com>
Link: https://lore.kernel.org/r/20220203102900.528987-1-steen.hegelund@microchip.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>