avutil/get_pool: remove dead operations whichs result is never used.

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

libavutil/buffer.c

@@ -242,7 +242,7 @@ static BufferPoolEntry *get_pool(AVBufferPool *pool)
     BufferPoolEntry *cur = *(void * volatile *)&pool->pool, *last = NULL;
 
     while (cur != last) {
-        FFSWAP(BufferPoolEntry*, cur, last);
+        last = cur;
         cur = avpriv_atomic_ptr_cas((void * volatile *)&pool->pool, last, NULL);
         if (!cur)
             return NULL;