aio: use kmem_cache_free() instead of kfree()

memory allocated by kmem_cache_alloc() should be freed using
kmem_cache_free(), not kfree().

Fixes: fa0ca2aee3 ("deal with get_reqs_available() in aio_get_req() itself")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/aio.c

@@ -1034,7 +1034,7 @@ static inline struct aio_kiocb *aio_get_req(struct kioctx *ctx)
 		return NULL;
 
 	if (unlikely(!get_reqs_available(ctx))) {
-		kfree(req);
+		kmem_cache_free(kiocb_cachep, req);
 		return NULL;
 	}