ibmvnic: free reset-work-item when flushing

Fix a tiny memory leak when flushing the reset work queue.

Fixes: 2770a798 ("ibmvnic: Introduce hard reset recovery")
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>