cxgb4: Fix for SR-IOV VF initialization

Commit 35b1de55

 ("rdma/cxgb4: Fixes cxgb4 probe failure in VM when PF is exposed
through PCI Passthrough") introduced a regression, where VF failed to
initialize for Physical function 0 to Physical Function 3. In the above
commit, we removed the code which used to enable sriov for PF0 to PF3. Now
adding it back to get sriov working.

V2:
 Removed SRIOV loop for PF[0..3] to instantiate the VF's as per David Miller's
 comment

Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>