curl_ntlm_core: use Curl_raw_toupper instead of toupper

This was the only remaining use of toupper in the entire source code.

Suggested-by: Daniel Stenberg

lib/curl_ntlm_core.c

@@ -522,7 +522,7 @@ static void ascii_uppercase_to_unicode_le(unsigned char *dest,
 {
   size_t i;
   for(i = 0; i < srclen; i++) {
-    dest[2 * i] = (unsigned char)(toupper((unsigned char)src[i]));
+    dest[2 * i] = (unsigned char)(Curl_raw_toupper(src[i]));
     dest[2 * i + 1] = '\0';
   }
 }