bnx2x: avoid null pointer dereference when enabling SR-IOV

Fixed NULL pointer dereference when dynamically activating SR-IOV after vf
database failed to be allocated in probe stage (for example due to no ARI
support in pci hub).

Signed-off-by: Michal Kalderon <michals@broadcom.com>
Signed-off-by: Ariel Elior <ariele@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>