enic: fix compile when CONFIG_PCI_IOV is not enabled

reverting back change that access enic->num_vfs outside
CONFIG_PCI_IOV

Reported-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Roopa Prabhu <roprabhu@cisco.com>
Signed-off-by: David S. Miller <davem@davemloft.net>