i40evf: do not re-arm watchdog after remove

Add in an adapter state check to prevent re-arming watchdog timer after
i40evf_remove has been called and timer has been deleted.

Change-ID: I636ba7c6322be8cbf053231959f90c0a2d8d803a
Signed-off-by: Ashish Shah <ashish.n.shah@intel.com>
Tested-by: Sibai Li <sibai.li@intel.com>
Signed-off-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>