net: dsa: mv88e6xxx: add an error code check in mv88e6352_tai_event_work

mv88e6xxx_tai_write() can return error code (-EOPNOTSUPP ...) if failed.
So check the value of 'ret' after calling mv88e6xxx_tai_write().

Signed-off-by: Su Hui <suhui@nfschina.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>