net: lan9303: Fix read error execution path

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: a1292595 ("net: dsa: add new DSA switch driver for the SMSC-LAN9303")
Signed-off-by: Jerry Ray <jerry.ray@microchip.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20221209153502.7429-1-jerry.ray@microchip.com


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