constify values from WS_Printf()

src/pattern.c

@@ -127,7 +127,7 @@ validation_init(void)
 const char *
 valid(VRT_CTX, const char * restrict const path)
 {
-	char *errmsg = NULL;
+	const char *errmsg = NULL;
 	int r, ovector[6];
 	size_t len;
 

src/vmod_hoailona.c

@@ -725,7 +725,7 @@ vmod_hosts_explain(VRT_CTX, struct vmod_hoailona_hosts *hosts,
 	struct policy_task *task;
 	struct host *host;
 	struct vmod_hoailona_policy *policy;
-	char *ret = NULL;
+	VCL_STRING ret = NULL;
 
 	CHECK_OBJ_NOTNULL(ctx, VRT_CTX_MAGIC);
 	CHECK_OBJ_NOTNULL(ctx->ws, WS_MAGIC);