This patch fixes an issue where a read failure of a port statistic counter
will return unknown results. While it is highly unlikely the read will
ever fail, it is much cleaner to return a zero for the stat count.
Fixes: a1292595e006 ("net: dsa: add new DSA switch driver for the SMSC-LAN9303")
Signed-off-by: Jerry Ray <jerry.ray@xxxxxxxxxxxxx>