qlcnic: Fix panic while setting VF's MAC address

o "qlcnic_sriov" structure pointer should be accessed only
  when SR-IOV is enabled. Access this pointer after SR-IOV
  PF check.

Signed-off-by: Manish Chopra <manish.chopra@qlogic.com>
Signed-off-by: Sucheta Chakraborty <sucheta.chakraborty@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>