__generic_file_write_iter(): fix handling of sync error after DIO

commit 60bb4529 upstream.

If DIO results in short write and sync write fails, we want to bugger off
whether the DIO part has written anything or not; the logics on the return
will take care of the right return value.
Reported-by: Anton Altaparmakov <aia21@cam.ac.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

mm/filemap.c

@@ -2584,7 +2584,7 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 		 * that this differs from normal direct-io semantics, which
 		 * will return -EFOO even if some bytes were written.
 		 */
-		if (unlikely(status < 0) && !written) {
+		if (unlikely(status < 0)) {
 			err = status;
 			goto out;
 		}