ShellPkg/UefiShellAcpiViewCommandLib: Fix VS2012 build failure

Fix following build error:
UefiShellAcpiViewCommandLib\AcpiParser.c(519) :
error C2308: concatenating mismatched strings
Concatenating wide "ERROR: %a: Offset Mismatch for %s"
with narrow "CurrentOffset = %d FieldOffset = %d"

cc: Alexei Fedorov <Alexei.Fedorov@arm.com>
cc: Ruiyu Ni <ruiyu.ni@intel.com>
cc: Jaben Carsey <jaben.carsey@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>

ShellPkg/Library/UefiShellAcpiViewCommandLib/Parsers/Dbg2/Dbg2Parser.c

@@ -120,7 +120,7 @@ ValidateNameSpaceStrLen (
     IncrementErrorCount ();
     Print (
       L"\nERROR: NamespaceString Length = %d. If no Namespace device exists,\n"
-       "    then NamespaceString[] must contain a period '.'",
+       L"    then NamespaceString[] must contain a period '.'",
       NameSpaceStrLen
       );
   }