io_uring: fix build warning on arm

./include/linux/socket.h:380:38: warning: 'struct file' declared inside parameter list will not be visible outside of this definition or declaration
  380 | extern int __sys_accept4_file(struct file *file, unsigned file_flags,
      |                                      ^~~~

Fixes: d7d134b7 ("net: add __sys_accept4_file() helper")
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Reviewed-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

include/linux/socket.h

@@ -13,6 +13,7 @@
 struct pid;
 struct cred;
 struct socket;
+struct file;
 
 #define __sockaddr_check_size(size)	\
 	BUILD_BUG_ON(((size) > sizeof(struct __kernel_sockaddr_storage)))