UefiExt: Use String Len Not Sizeof

When calculating what to print when a truncated message is
sent from the debugger, UefiExt was using sizeof(CHAR8 *)
which ended up removing valid characters that the target
debugger had sent.

This fixes it to use the length, not size of the pointer.

Author: os-d

UefiDbgExt/swdebug.cpp

@@ -174,7 +174,7 @@ monitor (
     if (Len > TruncateTagLen) {
       if (strncmp (Response + Len - TruncateTagLen, TruncateTag, TruncateTagLen) == 0) {
         // The response was truncated, so we need to read more.
-        Response[Len - sizeof (TruncateTag)] = 0; // Remove the truncate tag.
+        Response[Len - TruncateTagLen] = 0; // Remove the truncate tag.
         dprintf ("%s", Response);
         Offset += Len - TruncateTagLen;
         continue;