fs/afs: use struct_size() in kzalloc()

As Gustavo said in other patches doing the same replace, we can now
use the new struct_size() helper to avoid leaving these open-coded and
prone to type mistake.

Signed-off-by: Zhengyuan Liu <liuzhengyuan@kylinos.cn>
Signed-off-by: David Howells <dhowells@redhat.com>

fs/afs/write.c

@@ -48,8 +48,7 @@ static int afs_fill_page(struct afs_vnode *vnode, struct key *key,
 		return 0;
 	}
 
-	req = kzalloc(sizeof(struct afs_read) + sizeof(struct page *),
-		      GFP_KERNEL);
+	req = kzalloc(struct_size(req, array, 1), GFP_KERNEL);
 	if (!req)
 		return -ENOMEM;