ixgbevf: use pci drvdata correctly in ixgbevf_suspend()

We had set the pci driver-specific data in ixgbevf_probe() as a type of
struct net_device, so we should use it as netdev in ixgbevf_suspend().

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>