net: dsa: b53: Add missing ARL entries for BCM53125

The BCM53125 entry was missing an arl_entries member which would
basically prevent the ARL search from terminating properly. This switch
has 4 ARL entries, so add that.

Fixes: 1da6df85 ("net: dsa: b53: Implement ARL add/del/dump operations")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>