io_uring: use a rwf_t for io_rw.flags

Use the proper type.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220518084005.3255380-2-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -640,7 +640,7 @@ struct io_rw {
 	struct kiocb			kiocb;
 	u64				addr;
 	u32				len;
-	u32				flags;
+	rwf_t				flags;
 };
 
 struct io_connect {