[PATCH v3] OvmfPkg/QemuBootOrderLib: Fix NOOPT build failure

[Dandan Bi <dandan.bi@intel.com>]

This patch is to fix the IA32/NOOPT/VS Toolchain build failure.
The VS2015 failure log as below:
QemuBootOrderLib.lib(ExtraRootBusMap.obj) : 
error LNK2001: unresolved external symbol __allmul
s:\..\Build\OvmfIa32\NOOPT_VS2015\IA32\MdeModulePkg\
Universal\BdsDxe\BdsDxe\DEBUG\BdsDxe.dll : 
fatal error LNK1120: 1 unresolved externals
NMAKE : fatal error U1077: 
'"C:\Program Files\Microsoft Visual Studio 14.0\Vc\bin\link.exe"' : 
return code '0x460'
Stop.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Dandan Bi <dandan.bi@intel.com>

Notes:
  V3: Add VS compiler error message in commit log.

---
 OvmfPkg/Library/QemuBootOrderLib/ExtraRootBusMap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/OvmfPkg/Library/QemuBootOrderLib/ExtraRootBusMap.c b/OvmfPkg/Library/QemuBootOrderLib/ExtraRootBusMap.c
index ec42214..70ba161 100644
--- a/OvmfPkg/Library/QemuBootOrderLib/ExtraRootBusMap.c
+++ b/OvmfPkg/Library/QemuBootOrderLib/ExtraRootBusMap.c
@@ -306,8 +306,8 @@ MapRootBusPosToBusNr (
     return EFI_INVALID_PARAMETER;
   }
   if (RootBusPos > ExtraRootBusMap->Count) {
     return EFI_NOT_FOUND;
   }
-  *RootBusNr = ExtraRootBusMap->BusNumbers[RootBusPos - 1];
+  *RootBusNr = ExtraRootBusMap->BusNumbers[(UINTN)RootBusPos - 1];
   return EFI_SUCCESS;
 }
-- 
1.9.5.msysgit.1