ocelot: Cancel delayed work before wq destruction

Make sure the delayed work for stats update is not pending before
wq destruction.
This fixes the module unload path.
The issue is there since day 1.

Fixes: a556c76a ("net: mscc: Add initial Ocelot switch support")

Signed-off-by: Claudiu Manoil <claudiu.manoil@nxp.com>
Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>