switch {__,}blockdev_direct_IO() to iov_iter

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/btrfs/inode.c

@@ -7483,8 +7483,7 @@ static ssize_t btrfs_direct_IO(int rw, struct kiocb *iocb,
 
 	ret = __blockdev_direct_IO(rw, iocb, inode,
 			BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev,
-			iter->iov, offset, iter->nr_segs,
-			btrfs_get_blocks_direct, NULL,
+			iter, offset, btrfs_get_blocks_direct, NULL,
 			btrfs_submit_direct, flags);
 	if (rw & WRITE) {
 		if (ret < 0 && ret != -EIOCBQUEUED)