ntlm: avoid useless cast

ntlm: avoid useless cast

The argument passed to my_strupr() is converted to an upper case
string by means of toupper(). The latter expects a single signed int
as argument, therefore it makes sense to have my_strupr() take a
signed argument too and avoid an explicit and an implicit cast.

Signed-off-by: Antonio Quartulli <a@unstable.cc>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <20170710043441.24770-3-a@unstable.cc>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg15031.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 1cdfc9302aad8570360d278aded5fb9f110ca2b6)