net: pxa168_eth: Fix a potential data race in pxa168_eth_remove

Commit 0571a753 cancelled delayed work too late, keeping small
race. Cancel work sooner to close it completely.

Signed-off-by: Pavel Machek (CIP) <pavel@denx.de>
Fixes: 0571a753 ("net: pxa168_eth: Fix a potential data race in pxa168_eth_remove")
Signed-off-by: David S. Miller <davem@davemloft.net>