PCI: Remove redundant validation of SR-IOV offset/stride registers

Previously, we read, validated, and cached PCI_SRIOV_VF_OFFSET and
PCI_SRIOV_VF_STRIDE in sriov_enable().  But sriov_init() now does
that via compute_max_vf_buses(), so we don't need to do it again.

Remove the PCI_SRIOV_VF_OFFSET and PCI_SRIOV_VF_STRIDE config reads from
sriov_enable().  The pci_sriov structure already contains the offset and
stride corresponding to the current NumVFs.

[bhelgaas: split to separate patch for reviewability]
Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Wei Yang <weiyang@linux.vnet.ibm.com>