Fix declarations and constification for inline stack.

Reviewed-by: Richard Levitte <levitte@openssl.org>
diff --git a/test/ssltest.c b/test/ssltest.c
index 58e0f82..44d0019 100644
--- a/test/ssltest.c
+++ b/test/ssltest.c
@@ -1049,7 +1049,7 @@
 
     SSL_CONF_CTX *s_cctx = NULL, *c_cctx = NULL;
     STACK_OF(OPENSSL_STRING) *conf_args = NULL;
-    const char *arg = NULL, *argn = NULL;
+    char *arg = NULL, *argn = NULL;
 
     verbose = 0;
     debug = 0;