CryptoPkg: Fix unused variable in CryptX509.c

Without this change we get:

  error: variable 'Index' set but not used

when building on XCODE5.

Co-authored-by: Savva Mitrofanov <savvamtr@gmail.com>
Signed-off-by: Mike Beaton <mjsbeaton@gmail.com>

CryptoPkg/Library/BaseCryptLib/Pk/CryptX509.c

@@ -102,7 +102,6 @@ X509ConstructCertificateStackV (
 
   STACK_OF (X509)  *CertStack;
   BOOLEAN  Status;
-  UINTN    Index;
 
   //
   // Check input parameters.
@@ -124,7 +123,7 @@ X509ConstructCertificateStackV (
     }
   }
 
-  for (Index = 0; ; Index++) {
+  while (TRUE) {
     //
     // If Cert is NULL, then it is the end of the list.
     //