PCI: hv: Use pci_function_description[0] in struct definitions

The 2 structs can use a zero-length array here, because dynamic memory of
the correct size is allocated in hv_pci_devices_present() and we don't need
this extra element.

No functional change.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: KY Srinivasan <kys@microsoft.com>
CC: Jake Oshins <jakeo@microsoft.com>
CC: Haiyang Zhang <haiyangz@microsoft.com>
CC: Vitaly Kuznetsov <vkuznets@redhat.com>