io_uring: use io_file_from_index in __io_sync_cancel

Use io_file_from_index instead of open coding it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20230620113235.920399-7-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/cancel.c

@@ -216,13 +216,10 @@ static int __io_sync_cancel(struct io_uring_task *tctx,
 	/* fixed must be grabbed every time since we drop the uring_lock */
 	if ((cd->flags & IORING_ASYNC_CANCEL_FD) &&
 	    (cd->flags & IORING_ASYNC_CANCEL_FD_FIXED)) {
-		unsigned long file_ptr;
-
 		if (unlikely(fd >= ctx->nr_user_files))
 			return -EBADF;
 		fd = array_index_nospec(fd, ctx->nr_user_files);
-		file_ptr = io_fixed_file_slot(&ctx->file_table, fd)->file_ptr;
-		cd->file = (struct file *) (file_ptr & FFS_MASK);
+		cd->file = io_file_from_index(&ctx->file_table, fd);
 		if (!cd->file)
 			return -EBADF;
 	}