Move pcibios_sriov_disable() up so it's defined before a future use.

[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>