direct-io: eliminate the offset argument to ->direct_IO

Including blkdev_direct_IO and dax_do_io.  It has to be ki_pos to actually
work, so eliminate the superflous argument.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/mm/filemap.c b/mm/filemap.c
index e7108c3..cb36db9 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1853,8 +1853,7 @@
 					iocb->ki_pos + count - 1);
 		if (!retval) {
 			struct iov_iter data = *iter;
-			retval = mapping->a_ops->direct_IO(iocb, &data,
-					iocb->ki_pos);
+			retval = mapping->a_ops->direct_IO(iocb, &data);
 		}
 
 		if (retval > 0) {
@@ -2538,7 +2537,7 @@
 	}
 
 	data = *from;
-	written = mapping->a_ops->direct_IO(iocb, &data, pos);
+	written = mapping->a_ops->direct_IO(iocb, &data);
 
 	/*
 	 * Finally, try again to invalidate clean pages which might have been