avutil/add_to_pool: remove unused assgnment

Fixed CID991859
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/buffer.c

@@ -263,7 +263,7 @@ static void add_to_pool(BufferPoolEntry *buf)
     while (end->next)
         end = end->next;
 
-    while ((cur = avpriv_atomic_ptr_cas((void * volatile *)&pool->pool, NULL, buf))) {
+    while (avpriv_atomic_ptr_cas((void * volatile *)&pool->pool, NULL, buf)) {
         /* pool is not empty, retrieve it and append it to our list */
         cur = get_pool(pool);
         end->next = cur;