FatPkg/FatPei: Check array offset before use

Move the range check before array access to enforce the bounds
as expected.

Cc: Ray Ni <ray.ni@intel.com>
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>

FatPkg/FatPei/FatLiteApi.c

diff --git a/FatPkg/FatPei/FatLiteApi.c b/FatPkg/FatPei/FatLiteApi.c
index cc48c4c..b89ab70 100644
--- a/FatPkg/FatPei/FatLiteApi.c
+++ b/FatPkg/FatPei/FatLiteApi.c
@@ -459,7 +459,7 @@
       // Find corresponding physical block device

       //

       BlockDeviceNo = PrivateData->Volume[Index].BlockDeviceNo;

-      while (PrivateData->BlockDevice[BlockDeviceNo].Logical && BlockDeviceNo < PrivateData->BlockDeviceCount) {

+      while (BlockDeviceNo < PrivateData->BlockDeviceCount && PrivateData->BlockDevice[BlockDeviceNo].Logical) {

         BlockDeviceNo = PrivateData->BlockDevice[BlockDeviceNo].ParentDevNo;

       }