fix prototypes for aio_read and aio_write

include/aio.h

@@ -41,8 +41,8 @@ struct aiocb {
 #define LIO_WAIT 0
 #define LIO_NOWAIT 1
 
-int aio_read(struct aiocb *);
-int aio_write(struct aiocb *);
+ssize_t aio_read(struct aiocb *);
+ssize_t aio_write(struct aiocb *);
 int aio_error(struct aiocb *);
 ssize_t aio_return(struct aiocb *);
 int aio_cancel(int, struct aiocb *);