auth: Fix integer type in ssh_kbdint_clean()

Fixes T188

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>
(cherry picked from commit 1434b4a279)

src/auth.c

@@ -1369,7 +1369,7 @@ void ssh_kbdint_free(ssh_kbdint kbd) {
 }
 
 void ssh_kbdint_clean(ssh_kbdint kbd) {
-    int i, n;
+    size_t i, n;
 
     if (kbd == NULL) {
         return;