Fix a missed size_t variable declaration

pqueue_size() now returns a size_t, but the variable that gets returned
was still declared as an int.
Reviewed-by: NRich Salz <rsalz@openssl.org>

ssl/pqueue.c

@@ -144,7 +144,7 @@ pitem *pqueue_next(pitem **item)
 size_t pqueue_size(pqueue *pq)
 {
     pitem *item = pq->items;
-    int count = 0;
+    size_t count = 0;
 
     while (item != NULL) {
         count++;