auth: Fix integer type in ssh_kbdint_free()

Fixes T188

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>
(cherry picked from commit 66c4857c4a)

src/auth.c

@@ -1333,7 +1333,7 @@ ssh_kbdint ssh_kbdint_new(void) {
 
 
 void ssh_kbdint_free(ssh_kbdint kbd) {
-    int i, n;
+    size_t i, n;
 
     if (kbd == NULL) {
         return;