MdeModulePkg: Handle InitialVFs=0 case for SR-IOV

MdeModulePkg: Handle InitialVFs=0 case for SR-IOV

Per the section 3.3.5 SR-IOV spec v1.1, InitialVFs (0ch).
InitialVFs indicates to SR-PCIM the number of VFs that are initially associated with the PF.
The minimum value of InitialVFs is 0.

Below code is used to calculate SR-IOV reserved bus number,
if InitialVFs =0, it maybe calculate the wrong bus number in this case.
  LastVF = PFRid + FirstVFOffset + (PciIoDevice->InitialVFs - 1) * VFStride

we can fix it with below code:
 if (PciIoDevice->InitialVFs == 0) {
 PciIoDevice->ReservedBusNum = 0;
} else {
PFRid  = EFI_PCI_RID (Bus, Device, Func);
 LastVF = PFRid + FirstVFOffset + (PciIoDevice->InitialVFs - 1) * VFStride;
//
// Calculate ReservedBusNum for this PF
//
PciIoDevice->ReservedBusNum = (UINT16)(EFI_PCI_BUS_OF_RID (LastVF) - Bus + 1);
//
 // Calculate ReservedBusNum for this PF
//
 PciIoDevice->ReservedBusNum = (UINT16)(EFI_PCI_BUS_OF_RID (LastVF) - Bus + 1);
}

https://bugzilla.tianocore.org/show_bug.cgi?id=4069

Signed-off-by: Foster Nong <foster.nong@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>