Constify char* input parameters in apps code

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
diff --git a/apps/s_server.c b/apps/s_server.c
index c8666f5..864ac99 100644
--- a/apps/s_server.c
+++ b/apps/s_server.c
@@ -882,7 +882,7 @@
     STACK_OF(X509_CRL) *crls = NULL;
     X509 *s_cert = NULL, *s_dcert = NULL;
     X509_VERIFY_PARAM *vpm = NULL;
-    char *CApath = NULL, *CAfile = NULL, *chCApath = NULL, *chCAfile = NULL;
+    const char *CApath = NULL, *CAfile = NULL, *chCApath = NULL, *chCAfile = NULL;
     char *dpassarg = NULL, *dpass = NULL, *inrand = NULL;
     char *passarg = NULL, *pass = NULL, *vfyCApath = NULL, *vfyCAfile = NULL;
     char *crl_file = NULL, *prog;