ocelot: Clean up stats update deferred work

This is preventive cleanup that may save troubles later.
No need to cancel repeateadly queued work if code is properly
refactored.
Don't let the ethtool -s process interfere with the stat workqueue
scheduling.

Signed-off-by: Claudiu Manoil <claudiu.manoil@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>